Identification of conserved domains in the cell attachment proteins of the three serotypes of reovirus

Sequence analysis of reovirus serotype 1 (ST1) and 2 (ST2) S1 genome segment cDNAs identified several differences from previously reported versions of their sequences. The sequences reported here comprise 1463 and 1440 base pairs, respectively; for comparison, the ST3 S1 genome segment is 1416 nucleotides long. The serotype 1 and 2 σ 1 proteins are predicted to contain 470 and 462 amino acids, respectively; the ST3 σ 1 protein is 455 amino acids long. As previously observed, the ST1 and ST2 σ 1 proteins are much more closely related to each other than to that of ST3 (about 48 and 25% similarity, respectively, using a computer program that finds about 14% similarity among unrelated proteins). The sequences of the three S1 genome segments have diverged very extensively in all three codon positions, in some cases almost to the extent of randomness. Despite this, not only function but also shape and configuration have been retained (since the three σ 1 proteins can be incorporated efficiently into completely heterologous capsids). Seventy-nine amino acid residues are conserved among all three serotypes, many of them clustered into five regions in which one-third or more of the residues are triply conserved. These regions may represent functionally conserved domains involved in oligomerization, cell attachment, and hemagglutination.