Differing populations of intracisternal A-particle genes in myeloma tumors and mouse subspecies.

Intracisternal A-particle genes form a family of endogenous retrovirus-like genetic elements that are transcribed in mouse plasmacytomas (myeloma tumors). Two types of A-particle genes that can be differentiated by a sequence of 0.5 kilobase found in one type but not the other have been identified. Quantitative Southern blot analysis was used to measure the populations of different A-particle genes in DNAs from BALB/c mice, the Japanese subspecies Mus musculus subsp. molossinus, and myeloma tumors. The majority of the genes (715 copies per haploid genome or 76%) were found to be nearly identical except for small changes in conserved restriction enzyme sites. The second type of A-particle gene was much less abundant with 90 copies representing approximately 10%. The A-particle RNA in MOPC104E and MOPC315 was found to be colinear with a small portion of this latter type, comprising only 2% of the endogenous intracisternal A-particle sequences. Myeloma tumor DNA was found to have a two- to fourfold increase in the number of these genes, suggesting that the intracellular viruses have been activated to produce a double-stranded complementary DNA which subsequently integrated into the tumor genome. Analysis of M. musculus subsp. molossinus DNA revealed similar but shifted populations of A-particle genes, when compared with BALB/c DNA, except for the absence of a prominent EcoRI-HindIII band at 3.9 kilobases. This latter band, representing approximately 15% of the A-particle genes in BALB/c DNA, was shown to be a deletion variant of the most abundant gene family.