The Saccharomyces recombination protein Tid1p is required for adaptation from G2/M arrest induced by a double-strand break

Saccharomyces cells with a single unrepaired double-strand break (DSB) will adapt to checkpoint-mediated G2/M arrest and resume cell cycle progression. The decision to adapt is finely regulated by the extent of single-stranded DNA generated from a DSB. We show that cells lacking the recombination protein Tid1p are unable to adapt, but that this defect is distinct from any role in recombination. As with the adaptation-defective mutations yku70Δ and cdc5-ad, permanent arrest in tid1Δ is bypassed by the deletion of the checkpoint gene RAD9. Permanent arrest of tid1Δ cells is suppressed by the rfa1-t11 mutation in the ssDNA binding complex RPA, similar to yku70Δ, whereas the defect in cdc5-ad is not suppressed. Unlike yku70Δ, tid1Δ does not affect 5′-to-3′ degradation of DSB ends. The tid1Δ defect cannot be complemented by overexpressing the homolog Rad54p, nor is it affected in rad51Δ tid1Δ, rad54Δ tid1Δ, or rad52Δ tid1Δ double mutants that prevent essentially all homologous recombination. We suggest that Tid1p participates in monitoring the extent of single-stranded DNA produced by resection of DNA ends in a fashion that is distinct from its role in recombination.