Expression of murine leukemia virus envelope glycoprotein gp69/71 on mouse thymocytes. Evidence for two structural variants distinguished by presence vs absence of G(ix) antigen

Thymocytes of several mouse strains were tested for expression of the gp69/71 envelope component of murine leukemia virus by surface iodination (¹²⁵I), followed by immunoprecipitation and sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis. These strains included two congenic lines differing from their partner stocks with respect to expression of G(IX) antigen demonstrable in the cytotoxicity assay. It is concluded that two structural variants of gp69/71 can be expressed on mouse thymocytes, that these are distinguishable by a small difference in mobility in SDS gels, that one carries G(IX) antigen and the other not, that they are coded, or their expression is regulated, by different chromosomal loci that are not closely linked, and that both can be expressed together on the thymocytes of inbred mice. In the intact thymocyte plasma membrane, the sites of group specific antigen shared by the two gp69/71 variants, unlike the G(IX) type specificity carried by only one of them, are probably inaccessible to antibody.