Five gag-gene-encoded structural
proteins, designated p12, pp18, pp20, p30, and p10 were purified from replication-competent
avian reticuloendotheliosis-associated virus (REV-A) by high-performance liquid chromatography complemented with
chloroform-
methanol extraction and
sodium dodecyl sulfate-
polyacrylamide gel electrophoresis. Based on
amino acid composition and NH2- and COOH-terminal sequence analysis p12, pp18, p30, and p10 are distinct from one another, whereas pp20 is likely identical to pp18 in primary structure. The p12 was resistant to Edman degradation and was found to be myristylated at the NH2-terminal amino group. Sequence comparisons among the retrovirus family show that pp18/pp20 and p10 are, respectively, homologs of phospho-
proteins and
nucleic acid-
binding proteins. A comparison of terminal sequences with the nucleotide sequence of spleen necrosis virus (SNV) revealed that the gag genes of SNV and REV-A are highly conserved; together with the identification of REV-A gag-precursor
polyprotein, Pr60gag in immunoprecipitates of radiolabeled cell lysates, this comparison also led to the establishment of the organization of Pr60gag, viz., NH2-p12-pp18-p30-p10-OH. Sequence comparisons show that REV-A/SNV is related to mammalian type C viruses: the pp18-p30 region is most homologous to the macaque/colobus group and least to simian sarcoma virus (SSV), whereas both the 5'- and 3'-gag regions (i.e., p12 and p10) are clostest to SSV. Immunological studies using monospecific
antisera and Western-blot analysis showed that
antigenic determinants of REV-A p30 are conserved in most of mammalian type C and type D viruses, but those of REV-A p12 are shared only with simian
sarcoma-associated virus (SSAV) and endogenous viruses of macaques.