Microsatellite instability in yeast: Dependence on the length of the microsatellite

Abstract

One of the most common microsatellites in eukaryotes consists of tandem arrays [usually 15-50 base pairs (bp) in length] of the dinucleotide GT. We examined the rates of instability for poly GT tracts of 15, 33, 51, 99 and 105 bp in wild-type and mismatch repair-deficient strains of Saccharomyces cerevisiae. Rates of instability increased more than two orders of magnitude as tracts increased in size from 15 to 99 bp in both wild-type and msh2 strains. The types of alterations observed in long and short tracts in wild- type strains were different in two ways. First, tracts ≤51 bp had significantly more large deletions than tracts ≤33 bp. Second, for the 99- and 105-bp tracts, almost all events involving single repeats were additions; for the smaller tracts, both additions and deletions of single repeats were common.