The phylogenetic tree of MuLV gag genes. Dendrogram was constructed using deduced amino acid sequences of the entire gag gene of MuLV-1313 and 14 other full-length Gag sequences available in the databases. Note the evolutionary relationship of the highly conserved gag genes of the ecotropic Cas-Br-E and amphotropic MuLV-1313 viruses isolated from the wild mice of the Southern California regardless of their differences in their host range. Sequences used in the analysis include: AKV MuLV (J01998), MuLV- 1313 (AF411814), Cas-Br-E MuLV (X57540), Friend-57 MuLV (X02794), Friend FB29 MuLV (Z11128), Friend PVC211 MuLV (M93134), Friend (FrC6-A8F5 D88386), mink cell focus-forming virus 1233 (MCF1233, U13766), Moloney MuLV (J02255), radiation leukemia virus (RadLV, K03363), Rauscher MuLV (Rauscher, U94692), SL3-3 MuLV (AF169256) and solid-type reticulum cell sarcoma 19-6 MuLV (SRS 19-6, AF019230), HEMV (AY818896) and MDEV (AF053745). Note the segregation of MuLV- 1313 and Cas-Br-E MuLV on a distinct node of the phylogenetic tree.