Catalyzes viral DNA integration into the host chromosome, by performing a series of DNA cutting and joining reactions. The Rauscher and Friend erythroleukemia viruses contain two components. The spleen focus-forming virus (SFFV) is replication defective, and causes foci of proliferating erythroid cells in spleens of infected mice. The second component is a replication competent murine leukemia virus (MuLV) that serves as a helper virus for SFFV.