Abstract
Profiling of murine leukemia virus (MuLV) proteins by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS-PAGE) has revealed a low-molecular-weight protein which does not appear in the corresponding region of viral protein profiles obtained by gel filtration in 6 M guanidine hydrochloride. This protein species, termed p15(E), is easily demonstrable in MuLV isolates for which the viral p15 and p12 proteins have almost identical electrophoretic mobilities; this leaves a protein slightly larger than these two in the PAGE system unaccounted for in the gel filtration system. However, antiserum against the void volume fraction of the gel filtration eluate precipitated the p15(E) component from solubilized, radiolabeled virions, as shown by SDS-PAGE analysis of such immunoprecipitates. Comparative radioprecipitation analyses of this type revealed that for various MuLV isolates p15(E) was distinguishable from p15 in terms of serological reactivities, relative mobilities in gel electrophoresis, and relative efficiencies of labeling with individual amino acids. Thus it appears that, as is the case for avian oncornaviruses, MuLVs contain seven major structural proteins.