Effect of proviral insertion on transcription of the murine B2mb gene.

We describe three B2mb mutants caused by integration of retroviral proviruses into the B2m gene. All three insertions occurred within 500 base pairs of each other in the 5' end of the first intron of the B2mb gene. Mutant cell line i1 contained a nonfunctional Abelson murine leukemia virus-initiated transcript that spliced into B2mb exon II; mutant cell lines i7 and i18 contained transcripts complementary to B2mb exon 1. Both i1 and i7 also contained small amounts of wild-type B2mb transcript. The implications of these studies for the development of retroviral insertional mutagenesis as a strategy for cloning previously uncloned genes are discussed.