Evidence for Transposition of Dispersed Repetitive DNA Families in Yeast

Dispersed repetitive DNA sequences from yeast (Saccharomyces cerevisiae) nuclear DNA have been isolated as molecular hybrids in lambdagt. Related S. cerevisiae strains show marked alterations in the size of the restriction fragments containing these repetitive DNAs. "Ty1" is one such family of repeated sequences in yeast and consists of a 5.6 kilobase (kb) sequence including a noninverted 0.25 kb sequence of another repetitious family, "delta", on each end. There are about 35 copies of Ty1 and at least 100 copies of delta (not always associated with Ty1) in the haploid genome. A few Ty1 elements are tandem and/or circular, but most are disperse and show (along with delta) some sequence divergence between repeat units. Sequence alterations involving Ty1 elements have been found during the continual propagation of a single yeast clone over the course of a month. One region with a large number of delta sequences (SUP4) also shows a high frequency of sequence alterations when different strains are compared. One of the differences between two such strains involves the presence or absence of a Ty1 element. The novel joint is at one inverted pair of delta sequences.