Comparative analysis: intracellular precursor polyproteins of baboon endogenous retroviruses and human viral isolate HL23V
Journal of Virology
Intracellular precursor polyproteins of three baboon endogenous retrovirus (BaEV) isolates, m7, 455K, and BILN, were compared with the intracellular proteins of the type C human isolate HL23V by radioimmunoprecipitation, followed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and tryptic peptide analysis. Human and canine cells infected with m7-BaEV and canine thymus cells infected with BILN-BaEV were characterized by identical precursor polyproteins Pr85V", Pr70-719"9, Pr659"9,
... 0-719"9, Pr659"9, and gPr85env. Canine cells infected with 455K-BaEV consistently showed a slightly different pattern of precursor polyproteins. These included Pr85V", Pr7O9'9, Pr67gag, and gPr85env. By tryptic digest mapping of peptides containing [3H]leucine, m7-BaEV and 455K-BaEV were shown to be highly related. By comparison, mapping studies showed that BILN-BaEV was less highly related to m7-BaEV than was 455K-BaEV. Differences in these related BaEV isolates presumably reflected virus-specific differential cleavage of core protein precursors or alterations in polyprotein primary structure or both. Chase-incubated cells infected with BaEV also contained a stable, p28related polyprotein termed P72r". This polyprotein migrated upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis slightly slower than the major core protein precursor Pr70-719'9 and appeared to arise by posttranslational modification of Pr7O-719'9. Immunoprecipitation of extracts of HL23V-infected cells with antisera to simian sarcoma-simian-associated virus proteins and BaEV proteins confirmed that these cells contained two unrelated viral components, one that was similar to m7-BaEV or BILN-BaEV and a second that was related to simian sarcoma-simian-associated virus. Tryptic digest mapping of BaEV and HL23V precursor polyproteins suggested that the BaEV-like component of HL23V was more closely related to m7-BaEV than to 455K-BaEV or BILN-BaEV.