Reovirus-specific polypeptides: analysis using discontinuous gel electrophoresis

Genetic diversity in natural populations of mammalian reoviruses: tryptic peptide analysis of outer capsid polypeptides of murine, bovine, and human type 1 and 3 reovirus strains

We have studied the structural relationships between the outer capsid polypeptides of eight murine, bovine, and human isolates of type 1 and 3 mammalian reoviruses. Our results show that the outer capsid polypeptides of reoviruses isolated from different mammalian species, in different years and different geographical areas, have both conserved and unique methionine-containing tryptic peptides. We found that tryptic peptides from mu 1C polypeptides of two human, one murine, and two bovine type 3 isolates and one human and two bovine type 1 reoviruses are highly conserved. Our data show that only one tryptic peptide pattern of the mu 1C polypeptide (encoded by the M2 gene) was present in reoviruses isolated from the three different mammalian species. The mu 1C polypeptide of the type 3 Dearing strain contained one tryptic peptide not found in any other reovirus isolate examined. In marked contrast to the mu 1C polypeptides, the sigma 3 polypeptides (encoded by the S4 gene) of three type 1 and three type 3 isolates were divided into two patterns based on significant differences in their tryptic peptides. In addition, at least seven tryptic peptides were conserved among the sigma 3 polypeptides of all virus strains examined. The sigma 3 polypeptide of the type 3 Dearing strain was distinguishable from the sigma 3 polypeptides of all other strains examined. The one mu 1C and two sigma 3 tryptic peptide patterns were found to occur interchangeably in isolates of type 1 or type 3. About 1/3 of the tyrosine-containing tryptic peptides of sigma 1 polypeptides of four type 3 isolates examined were conserved. Comparison of peptide differences in sigma 1 polypeptides of these isolates showed that each had one or more unique tryptic peptides, suggesting that the S1 genes coding for these polypeptides had undergone genetic drift or, alternatively, that there are at least two tryptic peptide patterns present among the sigma 1 polypeptides of these isolates. Our results suggest that genetic drift and reassortment are the most likely explanation for the extensive genetic diversity found in natural populations of mammalian reoviruses.

A genetic map of reovirus: assignment of the newly defined mutant groups H, I, and J to genome segments

Mutants representing three previously undefined reovirus type 3 mutant groups have been isolated following backcross of suppressed pseudorevertants to wild type (R.F. Ramig and B.N. Fields, 1979, Virology 92, 155-167; R. Ahmed, P.R. Chakraborty, A.F. Graham, R.F. Ramig, and B.N. Fields, 1980, J. Virol. 34, 383-389). The prototype mutant of each of the three new mutant groups was mapped by analysis of genome segment segregation in intertypic recombinants derived from crosses between the type 3 ts mutants and ts mutants of type 1 or type 2. Segregation analysis revealed the location of the group H prototype mutant tsH(26/8) to be genome segment M1, that of the group I prototype mutant tsI(138) to be segment L3, and that of the group J prototype mutant tsJ(128) to be segment S1. Mapping of the group I and J lesions required the identification of suppressed ts lesions in some of the intertypic rcombinant clones.

Characterization of a temperature-sensitive defect of enterovirus type 70

The mechanism of the failure of enterovirus type 70 to replicate at a nonpermissive temperature (39 degrees C) was investigated, and the following results were obtained. (i) Viral RNA synthesis was not observed at 39 degrees C in LLC-MK2 cells, in accordance with our previous findings with primary monkey kidney cells (Miyamura et al., Intervirology 9:206-213, 1978). (ii) Shutoff of host cell macromolecular synthesis by virus infection was as efficient at 39 degrees C as at a permissive temperature (33 degrees C). This inhibitory effect similarly occurred even in the presence of guanidine hydrochloride. (iii) Viral protein synthesis proceeded in vivo at the nonpermissive temperature, and the rate of the protein synthesis was higher than that at the permissive temperature under the conditions in which sufficient viral mRNA had been accumulated. This was also confirmed by analyzing the intracellular proteins synthesized at the nonpermissive temperature by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which identified them as virus-specific proteins. (iv) When infected cells were incubated at 39 degrees C and then transferred to 33 degrees C, viral RNA synthesis took place even in the presence of cycloheximide. (v) Furthermore, in experiments performed with an in vitro cell-free assay system, viral polymerase activity was found in the membrane-bound preparation extracted from infected cells which had been incubated at 39 degrees C in the presence or absence of guanidine hydrochloride. These results indicate that early translation of mRNA proceeds normally at the nonpermissive temperature and that the temperature-sensitive defect resides in the transcriptional stage.

Polymorphism of the migration of double-stranded RNA genome segments of avian reoviruses

A number of field isolates of avian reovirus were characterized by analysis of the migration pattern of their genomic double-stranded RNA (dsRNA) segments upon polyacrylamide gel electrophoresis. Comparison of the various isolates has demonstrated (i) no relationship between serotype and migration of any individual dsRNA segment, (ii) marked polymorphism of migration patterns of all dsRNA segments among isolates of the same serotype as well as among different serotypes, (iii) no correlation between genotype and disease state, (iv) less marked variability in migration pattern from isolates within a restricted geographic locale compared to isolates from distant locales, (v) the presence of a single genotype in local outbreaks of disease, and (vi) the relative invariant migration of several dsRNA segments among the avian reoviruses, one of which (S1) may serve to distinguish the avian from the mammalian reoviruses.

Tryptic peptide analysis of outer capsid polypeptides of mammalian reovirus serotypes 1, 2, and 3

We studied the structural relationships among the outer capsid polypeptides of prototype strains of mammalian reovirus serotypes 1, 2, and 3 by tryptic peptide mapping. The micron1C polypeptide showed an extraordinary degree of conservation of its methionine-containing tryptic peptides. In contrast, the most abundant viral polypeptide, sigma 3, contained both conserved and unique methionine-containing tryptic peptides. The viral type-specific antigen, the sigma 1 polypeptide, contained both conserved and unique methionine- and tyrosine-containing tryptic peptides. These results suggested that the mammalian reovirus genome segments encoding each of the viral outer capsid polypeptides were derived from common ancestral segments which have diverged to different degrees.

Small reovirus-specific particle with polycytidylate-dependent RNA polymerase activity

We previously reported that virus-specific particles with polycytidylate [poly(C)]-dependent RNA polymerase activity accumulated at 30 degrees C in reovirus-infected cells. These particles sedimented heterogeneously from 300 to 550S and traversed through a 40% glycerol cushion to the pellet in 3 h at 190,000 x g. In the present report, we found that smaller particles with poly(C)-dependent RNA polymerase activity remained in the glycerol cushion. These smaller, enzymatically active particles, when purified, sedimented at 15 to 1S. They were spherical or triangular with a diameter of 11 to 12 nm. They were comprised mostly, and likely solely, of one reovirus protein, sigma NS. No particles with poly(C)-dependent RNA polymerase activity were found in mock-infected cells. Chromatography on the cation exchanger, CM-Sephadex, ascertained that sigma NS was the poly(C)-dependent RNA polymerase and showed its existence in two forms. In one form, it was enzymatically active and eluted from the column at 0.5 M KCl. In the enzymatically inactive state, it did not bind to the column. Our results suggest that the enzymatically active form of sigma NS carries a greater net positive charge than the inactive form. They also suggest that both forms of sigma NS are associated with a particle which has poly(C)-dependent RNA polymerase activity.

Different rat-derived transforming retroviruses code for an immunologically related intracellular phosphoprotein

Kirsten sarcoma virus (Ki-MSV) and Harvey sarcoma virus (Ha-MSV) are mouse-rat recombinant viruses that were originally isolated by experimental inoculation of rats with helper-independent mouse type C viruses. We have recently identified in cells transformed by Ki-MSV or Ha-MSV, a phosphoprotein, p21, coded for by Ki-MSV and Ha-MSV [Shih, T.Y., Weeks, M.O., Young, H.A. & Scolnick, E.M. (1979) Virology 95, in press]. The p21, which is not a virion structural protein, was identified with antisera prepared by transplantation in rats of syngeneic Ha-MSV- or Ki-MSV-transformed nonproducer cells. In this study, we have applied the same methodology to examine a purely rat sarcoma virus (RaSV), which was isolated in cell culture by using helper-independent rat type C viruses [Rasheed, S., Gardner, M.B. & Huebner, R.J. (1978) Proc. Natl. Acad. Sci. USA 75, 2972-2976]. We report here that this new, purely rat sarcoma virus apparently codes for a p29, which shares immunological determinants and common V-8 protease-generated peptides with the p21 of Ha-MSV. The data suggest that the RaSV has acquired genetic information with similar coding capacity to some rat genetic information with similar coding combinant viruses, Ki-MSV and Ha-MSV. Based on data obtained on the p21 of a mutant of Ki-MSV temperature-sensitive for the maintenance of transformation, we suggest that the gene in RaSV that codes for the p29 is also required for the maintenance of RaSV-induced fibroblast transformation.

Helper-independent mink cell focus-inducing strains of Friend murine type-C virus: potential relationship to the origin of replication-defective spleen focus-forming virus

Recent studies have indicated that both the replication-defective spleen focus-forming virus (SFFV) in the Friend virus complex and the helper-independent mink cell focus-inducing (MCF) viruses derived from AKR-murine leukemia virus (MuLV) are env gene recombinants between ecotropic virus and xenotropic virus. In an attempt to isolate additional env gene recombinants between Friend murine leukemia virus (F-MuLV) and xenotropic virus, we have inoculated cloned ecotropic F-MuLV into newborn NIH Swiss mice and analyzed MuLV released from preleukemic and leukemic spleens of infected mice. Two helper-independent MCF strains of F-MuLV have been isolated. Like the previously described AKR-MCF viruses, the Friend MCF viruses are env gene recombinants between an ecotropic virus (F-MuLV) and a mouse xenotropic virus, as shown by host range, interference pattern, and tryptic peptide analysis of the gp70s of these MuLV. Furthermore, RNA from the Friend MCF viruses hybridizes completely to cDNAsffv, a nucleic acid probe which detects that portion of SFFV which was not derived from P-MuLV. The ability to isolate replicating MCF viruses derived from F-MuLV FURTHER strengthens the parallels between the Friend erythroleukemia system and the AKR thymic leukemia system. Finally, the potential relationship of helper-independent env gene recombinants between F-MuLV and xenotropic virus to be highly leukemogenic SFFV is discussed.

Comparison of the genomic organization of Kirsten and Harvey sarcoma viruses

Current studies were undertaken to compare the genomes of Kirsten murine sarcoma virus (Ki-MuSV), Harvey murine sarcoma virus (Ha-MuSV), and the replication-defective endogenous rat virus to understand the function of these viral RNAs. Genome organization and sequence homology were studied by fingerprinting large RNase T1-resistant oligonucleotides and by cross-protecting homologous oligonucleotides against RNase A and T1 digestion with complementary DNA prepared from each of the other viral RNA. Ki-MuSV and Ha-MuSV were found to share an extensive series of rat-derived oligonucleotides begining ca. 1 kilobase (kb) from the 3' end and extending to within 1.5 kb of the 5'end of Ki-MuSV RNA. The total map distance covered in ca. 5.5 kb. The eight oligonucleotides covering the 1.5 kb at the 5' end of Ki-MuSV RNA were not found in Ha-MuSV RNA. Five out of these eight oligonucleotides, however, could be designated with certainty to be of rat virus origin. Since Ha-MuSV is 6.5 kb in size and Ki-MuSV is 8 kb in size, the major difference between them is the 1.5 kb from the replication-defective endogenous rat virus sequences at the 5' end of Ki-MuSV not present in Ha-MuSV. Consistent with the difference in the genome structure, these two sarcoma viral RNA'S yielded distinct major translation products in cell-free systems, I.E., A 50,000-dalton polypeptide (P50) from Ki-MuSV and a 22,000-dalton polypeptide (p22) from Ha-MuSV. These polypeptides may provide the necessary protein makers for identifying in vivo virus-coded proteins.

Further biochemical characterization, including the detection of surface glycoproteins, of human, calf, and simian rotaviruses

Polyacrylamide gel electrophoretic analysis of purified preparation of the simian rotavirus SA-11 indicated eight polypeptide components that migrated in a manner remarkably similar to those of the previously characterized human and calf rotaviruses. Analyses of preparations of single-shelled and double-shelled particles of human, calf, and simian an rotaviruses have also permitted assignment of the polypeptides to the inner or outer shells. The major components of the outer shells of each virus have been identified as glycoproteins, and the importance of this in terms of host cell specificity is discussed. Sensitivities of the various rotaviruses to acid, proteases, and glycosidases were also investigated.

Genome RNAs and polypeptides of reovirus serotypes 1, 2, and 3

The virus-specific double-stranded genome RNA and polypeptides present in virions and cells infected with the three mammalian reovirus serotypes have been examined by co-electrophoresis in several different polyacrylamide gel systems. The double-stranded RNA and polypeptide species previously described for type 3 Dearing were found to have corresponding species in the other serotypes examined. In each serotype several RNA and polypeptide species were found to have different electrophoretic mobilities from the corresponding RNA or polypeptide species of type 3 Dearing. The combination of electrophoretic variants among the RNAs and polypeptides of the reovirus serotypes gave electrophoretic markers in all 10 of the reovirus genes. The usefulness of these electrophoretic markers in "mapping" the reovirus genome is discussed.

Temperature-sensitive mutants of reovirus type 3: evidence for aberrant mu 1 and mu 2 polypeptide species

An analysis of reovirus-specific polypeptides in cells infected with temperature-sensitive mutants under permissive and nonpermissive conditions revealed the presence of (i) all the known viral polypeptides and (ii) aberrant migration of the mu 1 and mu 2 polypeptides in four groups of mutants.