SECRETION OF A MURINE RETROVIRAL ENV ASSOCIATED WITH RESISTANCE TO INFECTION

Fv4 is an endogenous defective murine leukaemia virus (MuLV) which exp resses high levels of an envelope protein (Env) closely related to tha t of the ecotropic class of MuLVs. Mice bearing the natural Fv4 gene o r a transgenic version are resistant to infection by ecotropic MuLVs. Fv4 mice secrete the surface peptide (SU) of the Fv4 Env in their seru m and this secreted Env can block infection of NIH3T3 cells. To study the secretion of Fv4, we metabolically labelled cells expressing Fv4 E nv or Env from infectious MuLVs and followed synthesis, glycosylation, proteolytic processing and secretion of Env species. We found no diff erence in the kinetics of synthesis or processing of Fv4 Env compared to the envelopes of infectious MuLVs, but Fv4 Env associated more weak ly with its transmembrane anchor and was shed from the surface of cell s.