RAD53, DUN1 and PDS1 define two parallel G(2)/M checkpoint pathways in budding yeast

Eukaryotic checkpoint genes regulate multiple cellular responses to DNA dam age. In this report, we examine the roles of budding yeast genes involved i n G(2)/M arrest and tolerance to UV exposure. A current model posits three gene classes: those encoding proteins acting on damaged DNA (e.g. RAD9 and RAD24), those transducing a signal (MEC1, RAD53 and DUN1) or those particip ating more directly in arrest (PDS1), Here, we define important features of the pathways subserved by those genes. MEC1, which we find is required for both establishment and maintenance of G(2)/M arrest, mediates this arrest through two parallel pathways. One pathway requires RAD53 and DUN1 (the 'RA D53 pathway'); the other pathway requires PDS1, Each pathway independently contributes similar to 50% to G(2)/M arrest, effects demonstrable after cdc 13-induced damage or a double-stranded break inflicted by the HO endonuclea se, Similarly, both pathways contribute independently to tolerance of UV ir radiation. How the parallel pathways might interact ultimately to achieve a rrest is not yet understood, but we do provide evidence that neither the RA D53 nor the PDS1 pathway appears to maintain arrest by inhibiting adaptatio n. Instead, we think it likely that both pathways contribute to establishin g and maintaining arrest.