Abstract
Preparations of the 30 x 103 mol. wt. protein (p30) of Rauscher murine leukaemia virus (R-MuLV) which had been purified to homogeneity as judged by gel electrophoresis in the presence of SDS and by amino-terminal amino acid analysis, showed considerable isoelectric heterogeneity. It was found that R-MuLV p30 polypeptide chains are easily converted in vitro into chains with more acidic isoelectric points. R-MuLV p30 polypeptides with different isoelectric points displayed the same set of 125I-labelled tryptic peptides. It is concluded that the charge heterogeneity of R-MuLV p30, as revealed in isoelectric focusing experiments, is not caused by genetic heterogeneity of the virus genome but by post-translational modification.