Evolution of mouse mammary tumor virus-related sequences in the human genome

The human genome contains numerous copies of elements with sequence homology to the mouse mammary tumor virus (MMTV). We have been interested in whether these elements are still actively transposing in the germ lines, and investigated this question by looking at restriction fragment patterns. Genomic DNA from humans and selected animals were digested with three different restriction enzymes and hybridized with five probes representative of five subgroups of the human MMTV-related elements. Two polymorphisms as well as two cases of sexual dimorphism were discovered in human DNA. The latter indicate the presence of at least two elements of the MMTV family on the Y chromosome. DNA samples from non-primate mammals were all unreactive. Both chimpanzee and rhesus monkey had restriction patterns of roughly the same number of bands and total intensity as humans. The number of differences in patterns between humans, and between humans and chimpanzee or rhesus monkey, were compatible with being caused by point mutations. The data indicate that these elements were actively spreading in the genome some time before the split between apes and Old World monkeys, while being relatively inactive, at least as to transpositions in the germ line, in later ages.