Envelope-like membrane glycoprotein. The envelope-like membrane glycoprotein gp55 is defective in its transport to the cell surface and remains associated predominantly with the rough endoplasmic reticulum (RER) membrane. It is almost not incorporated into virions. Host cell surface expression appears to be a prerequisite for its leukemogenicity (By similarity). Compared to other gammaretroviruses which possess 2 envelope proteins (gp70 and p15E), RSFFV gp55 corresponds to a gp70-p15E fusion protein with a deletion of a portion of p15E. It is encoded by the defective env gene of the virus. The Rauscher murine leukemia virus complex induces a rapid and fatal erythroleukemia in adult mice. It is the replication-defective spleen focus-forming virus (SFFV) contained in this complex that causes foci of proliferating erythroid cells in spleens of infected mice. The second component is a replication competent Rauscher murine leukemia virus (R-MuLV) that serves as a helper virus for SFFV. Spleens of infected mice also contain a third component, the Rauscher mink cell focus-inducing (R-MCF) virus.