Holliday junctions accumulate in replication mutants via a RecA homolog- independent mechanism

Abstract

The Holliday junction recombination intermediate, an X-shaped DNA molecule (xDNA), was analyzed at rDNA in mitotically growing yeast. In wild- type cells, xDNA is only detected at S phase, suggesting that recombination is stimulated to repair replication-related lesions. A search for mutations that increase the level of xDNA uncovered a gene encoding a subunit of DNA polymerase α. Systematic examination of replication mutants revealed that defects in polymerase α and δ but not the ε complex stimulate the level of xDNA. These xDNAs are Holliday junctions and not replication intermediates. The level of Holliday junctions is greatly reduced in rad52 mutants, but surprisingly, not in mutants defective in the three known mitotically expressed yeast RecA homologs.