The SI genes of the three serotypes of reovirus have been cloned and sequenced. The SI genes encode protein al, the protein against which serotype-specific neutralizing antibodies are directed; it is also the reovirus hemagglutinin and cell-attachment protein and is a major determinant of host range/tissue specificity and of the nature of the interaction of reovirus with cells of the immune system. The SI genes of serotypes 1, 2, and 3 are 1458, 1442, and 1416 nucleotides long, respectively. They possess untranslated regions 13, 13, and 12 nucleotides long at their 5' termini and 188, 229, and 36 nucleotides long at their 3' termini. They possess two open reading frames. The first starts with a "weak" initiation codon and extends for 418, 399, and 455 codons, respectively; this is the size expected for the al proteins. The other reading frame starts at a "strong" initiation codon about 70 residues downstream from the 5' terminus but extends for only about 120 codons, being terminated by 3 in-phase termination codons in all three genes. The proteins encoded by these short open reading frames are quite basic. The serotype 1 and 2 SI genes are much more closely related to each other (28% homology) than to the serotype 3 S1 gene (5% and 9% homology, respectively).These figures are based on direct homology calculations, adjusted for 25% random coincidence. Serologic evidence and hydrophobicity profiles agree that the arl proteins of serotypes 1 and 2 are much more closely related to each other (about 40% homology) than to that of serotype 3 (only about 20% homology). The fact that the serotype 1 and 2 SI genes are much more closely related to each other than to the serotype 3 SI gene is remarkable since for all other nine reovirus genes the serotype 1 and 3 genes are much more closely related to each other than to the serotype 2 gene. Mechanisms that may effect this remarkable evolutionary pattern are discussed.There are three serotypes of reovirus. As judged by the ability of their double-stranded RNAs to hybridize with each other under standardized conditions, serotypes 1 and 3 are closely related (about 70%), whereas serotype 2 is related to serotypes 1 and 3 only to the extent of about 10% (1). The individual genes of the three serotypes vary in their relatedness from those that are most closely related, the 3 L genes, to the gene that has diverged to the greatest extent during evolution-namely, the SI gene, which encodes protein al (1). Protein o4 is not only the most type-specific of all reovirus proteins but is also functionally of great importance. It is the protein against which the major neutralizing antibodies are formed (2); it is the hemagglutinin (3); it is the viral cellattachment protein (4); it is the major determinant of the nature of the interaction of reoviruses with cells, including cells of the immune system (5-7); and it also appears to be the reovirus protein that switches off host cell DNA synthesis (8).Remarkably, protein ol is present in reovirus particles to the extent of only 24 m...
The genes of the Dearing strain of reovirus serotype. 3, which consist of double-stranded RNA, have been cloned into pBR322 by tailing both strands ofeach gene with poly(A), transcribing them with reverse transcriptase, self-hybridizing the cognate plus and minus cDNA strands, incubating them with Ekcherichia coli DNA polymerase I to ensure that they are complete, and cloning the double-stranded cDNA molecules by standard procedures. The sequence of the cloned S2 gene has been determined. The sequences at the termini are exactly the same as those at the ends of the native double-stranded RNA gene.
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