Palmitoylation of the intracytoplasmic R peptide of the transmembrane envelope protein in Moloney murine leukemia virus

Previously it was reported that the 16-amino-acid (aa) C-terminal cytoplasm ic tail of Moloney murine leukemia virus (MoMLV) transmembrane protein Pr15 E is cleaved off during virus synthesis, yielding the mature, fusion active transmembrane protein p15E and the 16-aa peptide (R peptide or p2E). It re mains to be elucidated how the R peptide impairs fusion activity of the unc leaved Pr15E. The R peptide from MoMLV was analyzed by Tricine-sodium dodec yl sulfate-polyacrylamide gel electrophoresis and immunostained with antise rum against the synthetic 16-aa R peptide. The R peptide resolved with an a pparent molecular mass of 7 kDa and not the 4 kDa seen with the correspondi ng synthetic peptide. The 7-kDa R peptide was found to be membrane bound in MoMLV-infected NIH 3T3 cells, showing that cleavage of the 7-kDa R-peptide tail must occur before or during budding of progeny virions, in which only small amounts of the 7-kDa R peptide were found. The 7-kDa R peptide was p almitoylated since it could be labeled with [H-3]palmitic acid, which expla ins its membrane association, slower migration on gels, and high sensitivit y in immunoblotting. The present results are in contrast to previous findin gs showing equimolar amounts of R peptide and p15E in virions. The discrepa ncy, however, can be explained by the presence of nonpalmitoylated R peptid e in virions, which were poorly detected by immunoblotting. A mechanistic m odel is proposed. The uncleaved R peptide can, due to its lipid modificatio n, control the conformation of the ectodomain of the transmembrane protein and thereby govern membrane fusion.