STABILIZATION OF MICROSATELLITE SEQUENCES BY VARIANT REPEATS IN THE YEAST SACCHAROMYCES-CEREVISIAE

We examined the effect of a single variant repeat on the stability of a 51-base pair (bp) microsatellite (poly GT). We found that the insert ion stabilizes the microsatellite about fivefold in wild-type strains. The stabilizing effect of the variant base was also observed in strai ns with mutations in the DNA mismatch repair genes pms1, msh2 and msh3 , indicating that this effect does not require a functional DNA mismat ch repair system. Most of the microsatellite alterations in the pms1, msh2 and msh3 strains were additions or deletions of single GT repeats , but about half of the alterations in the wild-type and msh6 strains were large (>8 bp) deletions or additions.