Molecular Biology of Rotaviruses I. Characterization of Basic Growth Parameters and Pattern of

Transcription

1 JOURNAL OF VIROLOGY, Aug. 1981, p Vol. 39, No X/81/ $02.00/0 Molecular Biology of Rotaviruses I. Characterization of Basic Growth Parameters and Pattern of Macromolecular Synthesis M. A. McCRAE* AND G. P. FAULKNER-VALLE Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL United Kingdom Received 10 March 1981/Accepted 27 April 1981 The United Kingdom tissue-adapted bovine rotavirus growing in African green monkey kidney (BSC-1) cells was selected as a model system with which to study the detailed molecular virology of rotavirus replication. Study of the kinetics of infectious virus production revealed a fairly rapid replication cycle, with maximum yield of virus after 10 to 12 h at 37 C. Progeny genome synthesis was first detected during the virus latent period at 2 to 3 h postinfection. Study of the kinetics of viral polypeptide synthesis showed that virus rapidly inhibited cellular polypeptide synthesis such that by 4 h postinfection, only virus-induced polypeptides, 15 of which were detected, were being synthesized. No qualitative changes in the pattern of viral polypeptide synthesis were observed during infection, although, based on kinetic synthesis, three quantitative classes of polypeptides were defined. Pulse-chase analysis revealed three post-translational changes in viral proteins, two of which were shown to be due to glycosylation. Tunicamycin inhibition studies were used to identify the putative non-glycosylated precursors of the two glycoproteins. Comparison of the infected-cell polypeptides with those present in purified virions revealed that most of the virus-induced proteins were incorporated into virions, with only VP9 being a truly nonstructural protein. Some localization of the various polypeptides within the purified virion was achieved by producing viral cores. Rotaviruses are a recently defined, ubiquitous group of viruses causing acute gastroenteritis in young animals of a wide variety of species (6, 14). Detailed molecular virological study of the group was initially hampered by difficulties in achieving routine propagation in vitro. However, more recently, a number of isolates have been adapted to tissue culture growth, allowing some basic facts about viral replication to be established (2, 5, 15, 20). It is clear that rotaviruses are members of the Reoviridae family and contain a genome of double-stranded RNA composed of 11 segments (7, 17, 18, 23, 24) ranging in molecular weight from approximately 2.0 x 106 to 0.4 x 106. Studies on the numbers and sizes of viral polypeptides have, however, yielded conflicting data (3, 8, 12, 16-19, 22). We wished to study the detailed molecular virology of this important virus group by using the United Kingdom tissue culture-adapted bovine rotavirus as a model system. The studies reported here were designed to characterize the basic growth parameters of this system and to define the kinetics of viral macromolecular synthesis after viral infection. MATERIALS AND METHODS Cells and virus growth. A sample of the Compton United Kingdom tissue culture-adapted bovine rotavirus that had been passed 19 times in LLCMK2 cells was obtained from M. Thouless. The virus was plaque purified twice in BSC-1 cells before use. Virus was grown by infecting confluent monolayers of BSC-1 cells with virus at a multiplicity of infection of <0.1 PFU per cell. After adsorption, the cells were overlaid with medium containing 10 ytg of trypsin per ml, and virus was harvested after 48 h. Virus production was quantitated by plaque assay on BSC-1 cells. No trypsin was used in the plaque assay, since it had no significant effect on viral plaque production. Routinely, plaque assays were read after 5 days of incubation at 37 C. Viral infection for analyzing kinetics of infection and viral macromolecular synthesis. Singlestep growth conditions were achieved by infecting confluent monolayers of BSC-1 cells with virus at a multiplicity of infection of 10 to 20. After adsorption for 1 h at 37 C, the infected monolayers were overlaid with medium containing 2% fetal calf serum. To construct virus growth curves, samples were harvested at the appropriate times postinfection into the medium. The kinetics of viral RNA synthesis were followed by using pulse-labeling for 1-h periods throughout infection with 32Pi at 1 mci/ml in phosphate-free medium. Pulse-labeling for the analysis of viral protein synthesis was done by using [35S]methionine at 1 mci/ml in phosphate-buffered saline for 15 min. When chase samples were required, the radioactive label was removed at the end of the pulse and replaced with medium containing 100 times the normal methionine 490

2 VOL. 39, 1981 MOLECULAR BIOLOGY OF ROTAVIRUSES Log, 6 pfu 4- A concentration. Chase samples were harvested after another 2 h of incubation at 37 C. Viral glycoprotein production was analyzed by labeling with [3H]glucosamine at 100,uCi/ml at 4 to 7 h postinfection. In experiments in which tunicamycin was used, it was present from the beginning of adsorption until the harvesting of the particular sample at a final concentration of 5,ug/ml. In all radioactive labeling experiments, samples were harvested by scraping the cells into 0.25 ml of 50 mm Tris (ph 8.0) and stored at -70 C until analyzed. Growth and purification of radioactively labeled virus. Confluent 80-oz (2.4-liter) roller bottles of BSC-1 cells were infected at a multiplicity of infection of 10, and after adsorption, growth was allowed to proceed for 4 to 5 h at 37 C in medium lacking methionine, so that the system would be depleted of methionine. This medium was then replaced by 35 ml of methionine-free medium containing 20 MCi of [35S]methionine per ml, and virus growth was allowed to proceed for 48 h at 37 C, by which time all the cells had become detached from the glass. Virus was purified by using a modification of the reovirus purification procedure of Smith et al. (21). Briefly, cells were disrupted by freeze-thawing and then homogenized with a 1/4 volume of Freon 113 (trichlorotrifluoroethane). The phases were separated by low-speed centrifugation and the aqueous phase was decanted. The organic phase was reextracted by homogenization three times with 25 ml of resuspension buffer (50 mm Tris-hydrochloride [ph 8.0], 10 mm NaCl, 2 mm CaCl2, 1.5 mm,b-mercaptoethanol). The aqueous phases were combined, and the virus that was present was concentrated by centrifugation (100,000 x g, 30 min, 4 C). The virus pellet was resuspended in resuspension buffer, loaded onto a preformed CsCl gradient (p, 1.2 to 1.4 g/cm3), and centrifuged at 100,000 x g for 2 h at 40C. The p 1.36 viral band was collected by side puncture, concentrated by centrifugation, and suspended in 50 mm Tris (ph 8.0). Polyacrylamide gel electrophoresis. Viral polypeptides were analyzed on gradient polyacrylamide gels by using the Laemmli discontinuous buffer system (9), as previously described (13). Gels were exposed at II -FIr-IT II *1} ll 1-r Time (hrs) FIG. 1. Virus growth curves in BSC-1 cells. A B C D E F G -.NW* 4m 3 -dome, ow 400 -Maslow -WOW, do S=4'>_) 0#-- -Q 60r-- to ,9 FIG. 2. Analysis of the kinetics of viral doublestranded RNA synthesis. Pulse-labeling of infected cells with 32P and subsequent analysis of samples on polyacrylamide gels were carried out as described in the text. (A) Pulse-labeling of uninfected cells; (B) virus-infected cells pulse-labeled at 1 to 2 h postinfection; (C) virus-infected cells pulse-labeled at 2 to 3 h postinfection; (D) infected cells pulse-labeled at 3 to 4 h postinfection; (E) virus-infected cells pulse-labeled at 4 to 5 h postinfection; (F) virus-infected cells pulse-labeled at 5 to 6 h postinfection; (G) virusinfected cells pulse-labeled at 7 to 8 h postinfection. -70 C using either fluorography or image-intensifying screens, as described by Laskey and Mills (10). RESULTS Virus growth curves and effects on host macromolecular synthesis. The first parameter that should be measured before undertaking a detailed analysis of virus growth is a virus growth curve. Figure 1 shows virus growth curves constructed at 31, 37, and 39 C. At 37

3 492 McCRAE AND FAULKNER-VALLE A B C D E F G H J. VIROL. and 390C, there was little difference in the kinetics of virus growth, which did, however, proceed significantly slower at 31 C. Pulse-labeling at various times postinfection with the appropriate radioactive precursor was used to analyze the effect of viral infection on the overall levels of host macromolecular synthesis. Viral infection was found to have no significant effect on the overall levels of DNA, RNA, and protein synthesis (data not shown). Viral RNA synthesis. Having established the kinetics of infectious virus production under single-step growth conditions, we wished to relate this to the kinetics of viral macromolecular synthesis. Production of progeny doublestranded RNA was investigated by pulse-labeling cells with 32p for sequential 1-h periods throughout infection. The results (Fig. 2) showed that progeny genome synthesis was first detected in the period 2 to 3 h postinfection and continued throughout the remainder of the infectious cycle. No significant difference in the kinetics of production of the various genome segments was observed. There appeared to be an overproduction of genome segment 4 in these studies, but a more detailed quantitative analysis with gel systems with greater resolving capacity will be required to confirm and define this. Kinetics of viral protein synthesis in infected cells. The kinetics of viral protein synthesis in infected cells was investigated by carrying out pulse-labeling and pulse-chase-labeling experiments with [35S]methionine at various times after infection. Polyacrylamide gel analysis of these samples (Fig. 3) showed that virusspecific polypeptides were clearly being synthesized only 2 h after infection (Fig. 3, tracks C and D). By 4 h postinfection, cellular polypeptide synthesis had been strongly inhibited and replaced by viral protein synthesis (Fig. 3, tracks E and F), which continued unabated at later times postinfection (Fig. 3, tracks G and H). The nomenclature system adopted for Fig. 3 is of the type used by Mason et al. (11), whereby all new polypeptides seen in infected cells are given the prefix VP and are then numbered in order of decreasing molecular weight. We also used the suffix c for some polypeptides to denote situations in which that protein is thought to derive directly from the protein with the same number by a post-translational event detectable by pulse-chase analysis. This nomenclature system is not entirely satisfactory, but it avoids the 120K-a 1O0K- 80K- 60K- 40K- 20K- *VP1 VP2 *VP3 VP4 *VP5.VP6 VP7 VP7c VP8 IVP9 VP1o VPlOc VPll VPllc VP12 FIG. 3. Polyacrylamide gel analysis of the kinetics of viral polypeptide synthesis. Pulse and pulse-chase samples labeled with [35S]methionine were prepared as described in the text. Samples were analyzed on a 5 to 11% gradient polyacrylamide gel, as previously described (13). (A) Pulse-labeled uninfected cells; (B) 2-h chase sample ofpulse shown in (A); (C) virus-infected cells pulse-labeled at 2 h postinfection; (D) 2-h chase sample ofpulse shown in (C); (E) virus-infected cells pulse-labeled at 4 h postinfection; (F) 2-h chase sample ofpulse shown in (E); (G) virus-infected cells pulse-labeled at 6 h postinfection; (H) 2-h chase sample ofpulse shown in (G). Approximate molecular weight values derived by using reovirus polypeptide markers are given down the left-hand side of the figure.

4 VOL. 39, 1981 VPI-._ VP2--W VP3 _ VP4- VPx-._ VPV VP5 V P6-i- VP7c-. VP8-- VP9- A 0 0:E B C C_ 120K -m-*-80k --60K -: - 40K VPIOc-_ VPIIc _t -;t :S VPI2 -i - 20K.: :d 0000 FIG. 4. Polyacrylamide gel analysis of virus structural polypeptides. [35S]methionine-labeled virions were purified as described in the text. Samples were analyzed on a 4 to 10% gradient polyacrylamide gel to achieve better resolution of the VP3- VP4 region. (A) 2-h chase sample of virus-infected cells pulselabeled with [35S]methionine at 5 h postinfection; (B) [3S]methionine-labeled purified virions; (C) [35S]methionine-labeled purified viral cores prepared from purified virions by treatment with EDTA, as described in the text. Approximate molecular weight values are given down the right-hand side of the figure. confusion that follows the use by independent laboratories of apparent molecular weight values as a basis for nomenclature. Approximate molecular weight values for some of the viral proteins are given in Fig. 3 to facilitate cross comparisons with other systems. Pulse-chase labeling revealed three changes in protein mobility occurring during the chase period which might be attributed either to posttranslational cleavage of a primary gene product or to some post-translation modification, such as glycosylation. These changes occurred in polypeptide VP7, which had a slightly increased mobility after the chase period, and in the VP10 region, where one of the two bands of approximately equal intensity at the end of the pulse period disappeared during the chase, and the other increased in intensity. Finally, in the VP11 region, a minor polypeptide underwent a slight increase in mobility during the chase period. Comparison of the polypeptide profiles of samples labeled at different times postinfection failed to reveal any qualitative variation in the viral proteins being made. However, despite the apparent absence of an early-late switch in viral V MOLECULAR BIOLOGY OF ROTAVIRUSES 493 protein synthesis, some quantitative variations in the kinetics of synthesis of the different virusinduced proteins were seen. Three classes of polypeptides could be distinguished: those such as VP9, whose synthesis reached maximum rate by only 2 h postinfection; those whose synthesis did not reach maximum rate until 4 h postinfection (e.g., VP1); and a third class containing proteins such as VP6, whose level of synthesis continued to increase throughout infection. Virus structural proteins. Having established the pattern and kinetics of synthesis of the virus-induced proteins seen in infected cells, we wished to determine which proteins were incorporated into the virion. [3S]methionine-labeled virions were therefore purified, and their polypeptide profiles were compared with those seen in infected cells (Fig. 4, tracks A and B). This comparison showed that most of the virusinduced proteins were present in purified virions to some degree. The only proteins that were clearly nonstructural were VP9 and VP12. VP7, VP10, and VP11 were also absent from purified VPI VP2- VP3- VP4 A B C D E F -120K -1OOK -<80K -60K VP5- VP6- VP7 -, -<40K VP7c VP8-- VP9~ VPIO- VPIOc- X; '---20K FIG. 5. Polyacrylamide gel analysis of [3H]glucosamine-labeled samples to identify viral glycoproteins. [3H]glucosamine-labeled samples were prepared as described in the text. Samples were analyzed on a 3 to 9% gradient polyacrylamide gel that was overrun to enhance the resolution of VP3 and VP4. The overrunning resulted in the loss of VP11, VPlIc, and VP12 from the bottom of the gel, but none of these polypeptides gave any incorporation of labeled glucosamine. (A) [35S]methionine-labeled sample of virus-infected cells pulse-labeled at 6 h postinfection; (B) 2-h chase sample of the pulse shown in (A); (C) uninfected BSC-1 cells labeled for 3 h with [3H]glucosamine; (D) virus-infected cells labeled at 4 to 7 h postinfection with [3H]glucosamine; (E) [35S]methionine-labeled purified virions; (F) [36S]methioninelabeled viral cores prepared by EDTA treatment. Approximate molecular weight values are given down the right-hand side of the figure.

5 494 McCRAE AND FAULKNER-VALLE virions, although their respective chase products VP7c, VP1Oc, and VPllc were seen in virions. Conversely, only two structural polypeptides, VPX and VPY, were found to have no comigrating equivalents in virus-infected cells. It is possible that these proteins are formed in a maturation event of the type reported for Rous sarcoma virus (1), which occurs after cellular release, but the precursors from which they are produced remain unidentified. Treatment of purified rotavirions with chelating agents such as EDTA has been used by several groups (3, 11, 12, 19, 22) to remove the outer shell of the virion and give the denser rough particle. Purified virions were treated with 1.5 mm EDTA to remove the outer shell, and the viral cores were purified on a cesium chloride gradient. Cores produced by EDTA treatment were then analyzed on gradient polyacrylamide gels to determine which of the viral proteins composed the outer shell of the virion. The result (Fig. 4, track C) was clear-cut for several polypeptides, with VP4, VPY, and VP7c clearly being outer shell proteins and VP1, VP2, VP3, VPX, VP6, VP8, and VPllc always being present in viral core preparations. However, despite the fact that, morphologically, the outer shell was absent from all core preparations, the amounts of the other structural proteins remaining in the cores varied between preparations from as much as 70 to 80% to as little as 25 to 35%. Thus, even though it seems likely that these other proteins make up some part of the outer shell, the core preparation procedure available at present gives an equivocal answer concerning the locations of these proteins. Post-translational modification of viral A B C D E F G H J. VIROL. proteins. To investigate whether any of the virus-induced polypeptides was modified by glycosylation, cells were labeled with [3H]glucosamine. The result of a 3-h pulse-labeling revealed that three of the viral polypeptides, VP7, VP7c, and VP1Oc, were post-translationally modified by glycosylation (Fig. 5, track D) and that two of these, VP7c and VPlOc, comigrated with proteins found in purified virions (Fig. 5, track E). A comparison of the glucosamine labeling data with the data from [35S]methionine labeling (Fig. 3, tracks A and B; Fig. 5, tracks A and B) suggested that VP10 might be the non-glycosylated precursor of VP1Oc and that glycosylation was a relatively slow process whose occurrence could be charted by pulse-chase analysis. In contrast, such comparisons suggested no nonglycosylated precursors for VP7 and VP7c, although the kinetic studies (Fig. 3) did suggest that glycosylation occurred in two steps: a very fast one to generate the first glycosylation product, VP7, followed by a much slower VP7-to- VP7c conversion, which was revealed by pulse- 120 K- 100K_ 80 K- 60K 40K- 20K-- -VP I -VP2 -VP3 '-VP4 -VP5 - VP6,VP8 -VP9 - vpr7 -VPII - VPIIc - VP12 FIG. 6. Polyacrylamide gel analysis showing the effect of tunicamycin on the pattern of viral polypeptide synthesis. Samples were prepared as described in the text; for the uninfected cell sample pulse-labeled after tunicamycin treatment, cells were maintained in medium containing 5 pg of tunicamycin per ml for 5 h before labeling. Samples were analyzed on a 5 to 11% gradient polyacrylamide gel (13). (A) Uninfected BSC-I cells pulse-labeled with [35SJmethionine; (B) pulse-labeled uninfected cells maintained in the presence of tunicamycin; (C) virus-infected cells pulse-labeled at 4 h postinfection; (D) 2-h chase of sample shown in (C); (E) virus-infected cells maintained in the presence of tunicamycin and pulse-labeled at 4 h postinfection; (F) 2-h chase of sample shown in (E); (G) virus-infected cells maintained in the presence of tunicamycin and pulselabeled at 6 h postinfection; (H) 2-h chase of sample shown in (G). Approximate molecular weight values are given down the left-hand side of the figure.

6 VOL. 39, 1981 chase analysis. In an attempt both to confirm VP10 as the non-glycosylated precursor of VP10c and to identify the non-glycosylated precursor of VP7, we performed [35S]methionine pulse-chase experiments on infected cells that had been maintained in the presence of the glycosylation inhibitor tunicamycin. The results (Fig. 6) showed that, as we expected, tunicamycin blocked the formation of VP7 and VP7c and resulted in the appearance of a new polypeptide, vpr7, running slightly ahead of VP9. Based on this result, we postulated that vpr7 is the nonglycosylated precursor of VP7 and VP7c, which is normally very rapidly glycosylated either after or during its synthesis to generate VP7 and, therefore, is not detected in a normal 15-min pulse (Fig. 3). Tunicamycin also blocked the formation of both VP10 and VP10c and produced an increase in the labeling of VP12. The simplest interpretation of this result is that VP12 is the nonglycosylated precursor of VP10 which is further modified by a glycosylation step that includes the addition of the first glucosamine residue to generate VP10c. The kinetics of these proposed conversions revealed by the pulsechase experiments (Fig. 3) dictate that the initial VP12-to-VP10 step is either very slow or alternatively limited to only a fraction of VP12, since even after a 2-h chase, VP12 was clearly detectable in the infected cell profile (Fig. 3, tracks F and H). In Fig. 6, the synthesis of VP11 and VPllc also appears to be blocked by tunicamycin; a much longer exposure of the autoradiogram shown in Fig. 6 revealed, however, that although the level of synthesis of VP11 and VPllc was preferentially inhibited, the proteins were still synthesized with unchanged mobilities (data not shown). DISCUSSION The virus-cell system used in this study should provide a good model with which to study the detailed molecular virology of the rotaviruses. Virus replication, under single-step growth conditions, was rapid, with maximum virus yield obtained after only 10 to 12 h at 370C. The speed of the virus replication cycle found in this study was somewhat greater than has been previously reported for bovine rotavirus (12) or for the simian rotavirus SAl (5); this could be due either to the use of a different virus-cell combination or to the higher multiplicity of infection used in our study which would ensure a more synchronous infection. Viral infection was found to have no marked effect on the overall levels of cellular macromolecular synthesis, a finding which is in contrast to the situation seen with reovirus infection, which produces a marked inhibition of cellular DNA synthesis (4). Pulse-labeling studies with 32P showed, as ex- MOLECULAR BIOLOGY OF ROTAVIRUSES 495 pected, that progeny genome synthesis started during the latent period before the onset of infectious virus production. No qualitative differences in the time at which synthesis of individual segments started were observed, although more detailed analyses of the replication process will be necessary to establish whether synthesis of the different genome species is spatially separated, as in reovirus RNA replication (25). Several reports dealing with rotavirus polypeptides synthesized in infected cells have appeared (11, 12, 22). However, detailed studies of the kinetics of viral protein synthesis have been precluded in most cases by the poor shutoff of host protein synthesis. A direct comparison of our data with the data of previous reports is also hampered by our use of the higher-resolution gradient polyacrylamide gel system. These gels give increased resolution, particularly of the lower-molecular-weight polypeptides, and this probably accounts for the larger number of polypeptides resolved in our studies (11, 12, 22). Based on our in vivo analysis, we propose a number of precursor-product relationships VPI VpP 1(I) VP2 - - VP2(I) VP3 VP3(I) VP4 - VP4(o) VP x (I) VPY(o) VP5- VP5 VP6 M VP6(1) --:VPF7cVP7() VP9 VP vpr7 (G VPI2OC VP VOO VP loc _VPII,\GPI Ic _* VP llc ---V P12 Infected Cells Virions VP8 (i) (o) Proteins of the outer viral shell; (I) proteins FIG. 7. Scheme of virus-inducedpolypeptides seen in virus-infected cells and purified virions. This scheme is designed to show which virus-inducedpolypeptides seen in infected cells are also found in purified virions. It also gives our current hypotheses concerning the precursor-product relationships of the variousproteinsproduced bypost-translational modification; dotted arrows are used to indicateproposed initial glycosylation events. In some cases, the localization of virus structural polypeptides to the inner or outer shell of the virus was unequivocally achieved; these locations are indicated in parentheses. found in viral cores.

7 496 McCRAE AND FAULKNER-VALLE which are detailed in Fig. 7. If these relationships are substantiated by in vitro protein synthesis studies and partial peptide map analysis currently in progress, then the number of putative primary gene products seen in infected cells would be reduced to 11, commensurate with each segment of viral RNA being monocistronic, as seen with reovirus (13). Analysis of the virus structural proteins showed that only one primary gene product, VP9, appeared to be a true nonstructural protein, the remaining primary polypeptides or their modified products all being found in the virion to some degree. In contrast to the results of Rodger et al. (19), who found only one structural glycoprotein, both of the glycoproteins seen in infected cells in our study comigrated with virion structural proteins. This difference is probably due to the very small amounts of VPlOc present in virions, meaning that the presence of VP1Oc could have remained undetectable by the rather insensitive acid-schiff staining procedure (19). The use of chelating agents to remove the outer shell of the virus and thereby allow identification of the proteins making up this shell was not wholly satisfactory, since various amounts of some proteins were removed each time the viral cores were prepared. This variation means that, as indicated in Fig. 7, we were only able to locate some of the structural polypeptides precisely, and further work will be needed to locate the remainder defmitively. The variability of the core production procedure, coupled with our observation that some structural polypeptides appear to be degraded upon storage (M. A. McCrae, unpublished data), may at least partially account for the rather confused picture of the number and location of rotavirus structural proteins (3, 8, 11, 12, , 22). ACKNOWLEDGMEENTS We thank J. G. McCorquodale for providing expert technical assistance. This work was supported by grants from the Medical Research Council. ADDENDUM After this work was completed, a report by Espejo et al. (J. Virol. 37: , 1981) appeared, which showed that digestion of purified SAll with trypsin resulted in the cleavage of a polypeptide termed VP3, generating two smaller proteins termed VP5 and VP8. It is possible that VP5 is equivalent to either the VPX or VPY seen in our purified viral preparations. Experiments designed to investigate a possible precursor (VP3 and VP4)-product (VPX and VPY) relationship are currently in progress. LITERATURE CITED 1. Cheung, K. S., R. E. Smith, M. P. Stone, and W. K. Joklik Comparison of immature (rapid harvest) and mature Rous sarcoma virus particles. Virology 50: J. VIROL. 2. Clark, S. C., B. B. Barnett, and R. S. Spendlove Production of high-titer bovine rotavirus with trypsin. J. Clin. Microbiol. 9: Cohen, J., J. Laporte, A. Charpilienne, and R. Scherrer Activation of rotavirus RNA polymerase by calcium chelation. Arch. Virol. 60: Ensminger, W. D., and I. Tamm Cellular DNA and protein synthesis in reovirus infected L-cells. Virology 39: Estes, M. K., D. Y. Graham, C. P. Gerba, and E. M. Smith Simian rotavirus SAl1 replication in cell cultures. J. Virol. 31: Flewett, T. H., and G. N. Woode Rotaviruses. Arch. Virol. 57: Kalica, A. R., C. F. Garon, R. G. Wyatt, C. A. Mebus, D. H. Van Kirk, R. M. Chanock, and A. Z. Kapikian Differentiation of human and calf reovirus like agents associated with diarrhea using polyacrylamide gel electrophoresis of RNA. Virology 74: Kalica, A. R., and T. S. Theodore Polypeptides of simian rotavirus (SA 11) determination by a continuous polyacrylamide gel electrophoresis method. J. Gen. Virol. 43: Laemmli, U. K Cleavage of structural proteins during the assembly of the head of bacteriophage T4. Nature (London) 227: Laskey, R. A., and A. D. Mills Quantitative film detection of [3H] and [14C] in polyacrylamide gels by fluorography. Eur. J. Biochem. 66: Mason, B. B., D. Y. Graham, and M. K. Estes In vitro transcription and translation of simian rotavirus SAll gene products. J. Virol. 33: Matsuno, S., and A. Mukoyama Polypeptides of bovine rotavirus. J. Gen. Virol. 43: McCrae, M. A., and W. K. Joklik The nature of the polypeptide encoded by each of the 10 doublestranded RNA segments of Reovirus type 3. Virology 89: McNulty, M. S Rotaviruses. J. Gen. Virol. 40: McNulty, M. S., G. M. Allen, and J. B. McFerran Cell culture studies with a cytopathic bovine rotavirus. Arch. Virol. 54: Monette, J. P. L., M. M. Carpio, R. A. Kapitany, and L. A. Babiuk Polypeptide analysis of bovine rotavirus, p In Proceedings of the 2nd International Symposium on Neonatal Diarrhea. Veterinary Infectious Disease Organisation, Saskatoon, Saskatchewan, Canada. 17. Newman, J. F. E., F. Brown, J. C. Bridger, and G. N. Woode Characterization of a rotavirus. Nature (London) 258: Rodger, S. M., R. D. Schnagl, and I. H. Holmes Biochemical and biophysical characteristics of diarrhea viruses of human and calf origin. J. Virol. 16: Rodger, S. M., R. D. Schnagl, and L. H. Holmes Further biochemical characterization, including the detection of surface glycoproteins, of human, calf, and simian rotaviruses. J. Virol. 24: Smith, E. M., M. K. Estes, D. Y. Graham, and C. P. Gerba A plaque assay for the simian rotavirus SA 11. J. Gen. Virol. 43: Smith, R. E., H. J. Zweerink, and W. K. Joklik Polypeptide components of virions, top component and cores of Reovirus type 3. Virology 39: Thouless, M. E Rotavirus polypeptides. J. Gen. Virol. 44: Todd, D., and M. S. McNulty Characterization of pig rotavirus RNA. J. Gen. Virol. 33: Todd, D., and M. S. McNulty Biochemical studies on a reovirus-like agent (rotavirus) from lambs. J. Virol. 21: Zweerink, H. J Multiple forms of ss -. ds RNA polymerase activity in reovirus infected cells. Nature (London) 247: