Fre2, a proviral integration site of Friend murine leukemia virus that is closely linked to Fv2.

Friend murine leukemia virus (F-MuLV) induces leukemia by integration into the cellular genome, thereby changing the structure or expression of cellular oncogenes. In this report we describe a new F-MuLV integration site Fre2 isolated from splenic DNA of an erythroleukemic animal. This site was found to be rearranged in six out of 64 tumors tested; however, in five out of these six cases no F-MuLV proviruses could be detected in the vicinity of the rearrangement sites. The rearrangements represented closely clustered chromosomal breakpoints, presumably chromosomal translocations. Exons transcribed into differentially spliced mRNAs of 1.9 and 3.7 kb have been found near the breakpoint. Fre2 is closely linked to Fv2, a locus on mouse chromosome 9 involved in erythropoiesis. Sequences homologous to Fre2 could not be found in the gene databases.