Mutation and recombination in cattle satellite DNA: A feedback model for the evolution of satellite DNA repeats

The cattle genome contains several distinct centromeric satellites with int errelated evolutionary histories. We compared these satellites in Bovini sp ecies that diverged 0.2 to about 5 Myr ago. Quantification of hybridization signals by phosphor imaging revealed a large variation in the relative amo unts of the major satellites. In the genome of water buffalo this has led t o the complete deletion of satellite III. Comparative sequencing and PCR-RF LP analysis of satellites IV, 1.711a, and 1.711b from the related Bos and B ison species revealed heterogeneities in 0.5 to 2% of the positions, again with variations in the relative amounts of sequence variants. Restriction p atterns generated by double digestions suggested a recombination of sequenc e variants. Our results are compatible with a model of the life history of satellites during which homogeneity of interacting repeat units is both cau se and consequence of the rapid turnover of satellite DNA. Initially, a pos itive feedback loop leads to a rapid saltatory amplification of homogeneous repeat units. In the second phase, mutations inhibit the interaction of re peat units and coexisting sequence variants amplify independently. Homogeni zation by the spreading of one of the variants is prevented by recombinatio n and the satellite is eventually outcompeted by another, more homogeneous tandem repeat sequence.