R7, a spontaneous mutant of Moloney murine sarcoma virus 124 with three direct repeats and an in-frame truncated gag-mos gene, induces brain lesions.

We have isolated Recombinant 7 (R7), a spontaneous mutant of SV7, a molecular clone of MoMuSV124. Like SV7, R7 induces subcutaneous fibrosarcomas, spleen tumors, and mesentery tumors infiltrated by proliferating vessels lined by transformed endothelial cells. However, it also induces brain lesions. We have molecularly cloned and sequenced the R7 proviral DNA and shown that the R7 genome consists of 3401 bp. It has three direct repeats in each enhancer. Its coding sequence consists of only 176 bp of p15, 263 bp of p30, a 7-bp insertion, and 853 bp of an N-terminally truncated mos gene. From the sequence of R7 we have deduced that the truncated mos sequence is in-frame with all of the gag sequence and the 7-bp insertion. The incorporation of the 3' end of the p15 sequence further suggests that the R7 Gag-Mos is myristylated. We have also shown that the molecularly cloned R7 virus transformed NIH/3T3 fibroblasts about sevenfold better than the parental SV7. We have also confirmed that molecularly cloned R7 induces the same disease phenotype as that induced by the nonmolecularly cloned R7.