Antigenic differences among multiply charged Moloney murine leukemia virus p30 polypeptides found inside infected cells

At least three Moloney murine leukemia virus (M-MuLV) p30 polypeptides (p30's), viz., a major species at pI 6.3 and two minor ones at pI 6.1 and pI 6.6, have previously been identified in purified virions by 2-dimensional gel electrophoresis and chromatofocusing (Katoh, I., Yoshinaka, Y. and Luftig, R.B. (1984) J. Gen. Virol. 65, 733-741). We have observed a similar, but distinctive pI pattern for [35S]methionine-labeled MuLV p30's in lysates from chronically infected (MuLV) cells. The variation in pI pattern of the intracellular MuLV p30's was dependent on the type of p30 reactive antibody used for immunoprecipitation. Specifically: a p30 spot with pI 6.3 was always precipitated as the major spot with three different antibodies, minor spots with pI 6.0 and 6.6 were variably seen dependent on the antibody used, and an intracellular p30 spot at pI 6.1 was only precipitated with a rat p30 monoclonal antibody but not with monospecific mouse or intact MuLV cross-reacting p30 sera. These results indicate that first, there are differences between the pI pattern of virion and intracellular MuLV p30's, and second, the antigenic determinants of intracellular p30's vary dependent on the antibody used for immunoprecipitation.