Instability of the human minisatellite CEB1 in rad27Δ and dna2-1 replication-deficient yeast cells

Convergent studies in human and yeast model systems have shown that some minisatellite loci are relatively stable in somatic cells but not in the germline, and little is known about the mechanism(s) that can destabilize them. Unlike microsatellite sequences, mini satellites are not destabilized by mismatch repair mutations. We report here that the absence of Rad27 and Dna2 functions but not RNase H(35) or Exo1, which play an essential role in the processing of Okazaki fragments during replication, destabilize the human minisatellite CEB1 in mitotically growing Saccharomyces cerevisiae cells, up to 14% per generation in rad27Δ cells. Analysis using minisatellite variant repeat mapping by polymerase chain reaction of the internal structure of 17 variants reveals that the majority of rearrangements in rad27Δ cells are extremely complex contraction events that contain deletions, often accompanied by duplications of motif unit. Altogether, these results suggest that the improperly processed 5′ flap structures that accumulate when replication is impaired can act as a potent stimulator of minisatellite destabilization and can provoke an unexpectedly broad range of mutagenic events. This replication-dependent phenomenom differs from the recombination-induced instability in yeast meiotic cells.