A glycoprotein specified by spleen focus-forming virus in three cell lines varies on molecular size and peptide composition, but retains both xenotropic and ecotropic MuLV antigenicity.

A glycoprotein with an approx. mol. wt. of 55000, encoded by spleen focus-forming virus (SFFV), was detected with an antiserum against xenotropic murine leukaemia virus (MuLV) in various cell lines infected with the Friend strain of SFFV, suggesting that the SFFV-specific RNA coding for gp55 is related to the xenotropic virus. The proteins from three cell lines differed from each other in molecular size and gave different peptide maps. The differences in the gp55 molecules were shown to depend on differences in the SFFV genome, but not on differences in glycosylation or processing of the precursor polypeptides of gp55 in the different cells. These results indicate virus strain specificity of SFFV in gp55 formation.