Yeast genes involved in cadmium tolerance: identification of DNA replication as a target of cadmium toxicity

Cadmium (Cd2,) is a ubiquitous environmental pollutant and human carcinogen. The molecular basis of its toxicity remains unclear. Here, to identify the landscape of genes and cell functions involved in cadmium resistance, we have screened the Succharomyces cereuisiae deletion collection for mutants sensitive to cadmium exposure. Among the 4866 ORFs tested, we identified 73 genes whose inactivation confers increased sensitivity to Cd 2,. Most were previously unknown to play a role in cadmium tolerance and we observed little correlation between the cadmium sensitivity of a gene deletant and the variation in the transcriptional activity of that gene in response to cadmium. These genes encode proteins involved in various functions: intracellular transport, stress response and gene expression. Analysis of the sensitive phenotype of our Cd 21 -sensitive mutant collection to arsenite, cobalt, mercury and H202 revealed 17 genes specifically involved in cadmium-induced response. Among them we found RAD27 and subsequently DNA2 which encode for proteins involved in DNA repair and replication. Analysis of the Cd 2+ -sensitivity of RAD27 (rad27-G67S) and DNA2 (dna2-1) separation of function alleles revealed that their activities necessary for Okazaki fragment processing are essential in conditions of cadmium exposure. Consistently, we observed that wild-type cells exposed to cadmium display an enhanced frequency of forward mutations to canavanine resistance and minisatellite destabilisation. Taken together these results provide a global picture of the genetic requirement for cadmium tolerance in yeast and strongly suggest that DNA replication, through the step of Okazaki fragment processing, is a target of cadmium toxicity. (c) 2008 Elsevier B.V. All rights reserved.