A Comparative Study of the Phosphoproteins of the Endogenous Type C Retroviruses of Macaques and Colobus polykomos

Abstract

The phosphoproteins of the endogenous type C retroviruses of Macaques (MAC-1 and MMC-1) and Colobus polykomos (CPC-1) were isolated by the neutral chloroform-methanol extraction method and purified by reversed-phase high performance liquid chromatography (HPLC). During HPLC purification multiple forms of the phosphoproteins from each virus were detected. Two major forms of the MAC-1 and CPC-1 phosphoproteins were found while only one major form of the MMC-1 phosphoprotein was found. The MAC-1 and MMC-1 phosphoproteins migrated in sodium dodecylsulfate polyacrylamide gel electrophoresis (SDS-PAGE) with an apparent molecular weight of 16K. SDS-PAGE of the two major forms of the CPC-1 phosphoprotein produced two bands in each, a major one at 18K and a minor one at 20K. This 20K component was found to be an alternative form of the 18K component. Biochemical, primary structural, and immunological analyses were performed on these phosphoproteins. Compositional data indicated that the actual molecular mass of the peptide chain of these phosphoproteins is on the order of 9,500 daltons. Little or no differences in composition were detected between the phosphoproteins from MAC-1 and MMC-1, while slight compositional differences were observed between these and the CPC-1 phosphoproteins. Amino terminal amino acid sequencing demonstrated extensive sequence homology between these phosphoproteins thru the 37 sequenced positions. No differences in sequence were detected between the phosphoproteins of MAC-1 and MMC-1, while the phosphoproteins of CPC-1 differed from the other two in eight of the sequenced positions. Antiserums prepared against the MAC-1 phosphoprotein and the CPC-1 phosphoprotein were used to develop homologous and heterologous radioimmunoassays (RIAs). A panel consisting of type C and D retroviruses were tested in these RIAs. Only MAC-1, MMC-1, and CPC-1 were found to compete. In light of the highly variable nature of the viral phosphoprotein relative to the other structural proteins, the extensive similarities of these phosphoproteins clearly indicate that MAC-1, MMC-1, and CPC-1 are very closely related isolates. The Macaques and Colobus polykomos are separated by - 20 million years of evolution. This coupled with the closeness of the relationship between their endogenous retroviruses lends further support to the contention that the type C endogenous retroviruses of primates have stemmed from a common distant progenator.