Friend leukemia and mouse endogenous viruses: II. Proteins of Friend leukemia and mouse endogenous C-type particles produced by [formula omitted] mouse cell cultures

Abstract

The polypeptide patterns of con A-isolated Friend leukemia virus and other particles of density 1.18 that are spontaneously produced by Friend-infected and uninfected BALB c mouse cells are analyzed in high-resolution SDS-acrylamide gradient gels. Agglutination of virions by con A and fractionation of α-methyl mannose-dissociated complexes in sucrose equilibrium gradients yields a pattern associated with FLV (density 1.16) that contains at least 20 polypeptides of MW 30,000–218,000. The pattern includes the major structural polypeptide of MuLV, MW 34,000, and, compared to published patterns, it has a lower proportion of smaller polypeptides. Relative to serum albumin, a major component of culture medium, virion polypeptides are purified at least 50,000-fold, and the specific leukemia virus infectivity of isolates is approximately 1 PFU/800 particles. Though they are morphologically indistinguishable from FLV, and similarly contain viral 60–70 S RNA, spontaneously arising BALB c endogenous viruses (density 1.18) possess a recognizable complement of at least 26 polypeptides including a major one of MW 44,000. The pattern includes a glycopolypeptide of MW 14,000 that is not found in FLV. Like the FLV pattern, the majority of polypeptides are of MW 30,000–218,000. The greater number of polypeptides in endogenous virus suggests that the pattern may be derived from a mixture of particles, as suggested previously by others, and some evidence for mutual interaction between FLV and coproduced endogenous viruses is presented.