Reovirus S1 Research Articles

Biosynthesis of reovirus-specified polypeptides: the reovirus s1 mRNA encodes two primary translation products.

Reovirus serotypes 1 (Lang strain) and 3 (Dearing strain) code for a hitherto unrecognized low-molecular-weight polypeptide of Mr approximately 12,000. This polypeptide (p12) was synthesized in vitro in L-cell-free protein synthesizing systems programmed with either reovirus serotype 1 mRNA, reovirus serotype 3 mRNA, or with denatured reovirus genome double-stranded RNA, and in vivo in L-cell cultures infected with either reovirus serotype. The synthesis of p12 in vivo was insensitive to actinomycin D, and occurred at similar times after infection as the previously identified reovirus encoded lambda, mu, and sigma polypeptides. Pulse-chase experiments in vivo, and the relative kinetics of synthesis of p12 in vitro, indicate that it is a primary translation product. Fractionation of reovirus mRNAs by velocity sedimentation and translation of separated mRNAs in vitro suggests that p12 is coded for by the s1 mRNA, which also codes for the previously recognized sigma 1 polypeptide. Synthesis of both p12 and sigma 1 in vitro in L-cell-free protein synthesizing systems programmed with denatured reovirus genome double-stranded RNA also suggests that these two polypeptides can be coded by the same mRNA species. The Mr approximately 12,000 polypeptide was not a detectable structural component of purified virions, and antiserum prepared against purified reovirions did not immunoprecipitate p12. It is proposed that the Mr approximately 12,000 polypeptide encoded by the S1 genome segment be designated sigma 1bNS, and that the polypeptide previously designated sigma 1 be renamed sigma 1a.

Reovirus hemagglutinin mRNA codes for two polypeptides in overlapping reading frames.

Human reovirus s1 mRNA, which codes for the viral hemagglutinin, also directs the synthesis of a previously unrecognized polypeptide of molecular mass 14 kDa in reticulocyte and wheat germ extracts. Hybrid-arrest of translation by selected restriction fragments of cloned S1 DNA indicated that synthesis of the 14-kDa polypeptide initiates at the second AUG. This was confirmed by NH2-terminal sequence analyses. The coding sequence for the 14-kDa polypeptide thus lies entirely within the hemagglutinin gene but in a different reading frame. Although not found in virions, the 14-kDa polypeptide apparently is formed in virus-infected mouse L cells, as demonstrated by comparison of [35S]methionine-labeled polypeptides in cell extracts with the corresponding in vitro products.

Molecular cloning and sequencing of the reovirus (serotype 3) S1 gene which encodes the viral cell attachment protein sigma 1.

The complete sequence of the reovirus (serotype 3) S1 gene was obtained by using cloned cDNA derived from the RNA segment. This gene is 1416 nucleotides in length and contains two open reading frames. The first reading frame has a coding capacity of 455 amino acids, sufficient to account for the known S1 product, protein sigma 1 (42,000 MW). It possesses a signal peptide as well as three possible glycosylation sites. No homology could be detected when this gene sequence and the deduced amino acid sequence were compared to published sequences of the corresponding gene of a human rotavirus. The second reading frame (not in phase with the first) starts at the second ATG recently shown to be a functional initiation site. It has a coding capacity of 120 amino acids. Its outstanding feature is the highly basic amino-terminal region, a characteristic apparently shared by a number of DNA binding proteins. It is speculated that this protein, hitherto undetected, may play a role in mediating viral and/or host nucleic acid transcription.