SIR2 MUTANTS OF KLUYVEROMYCES-LACTIS ARE HYPERSENSITIVE TO DNA-TARGETING DRUGS

A Kluyveromyces lactis mutant, hypersensitive to the DNA-targeting dru gs ethidium bromide (EtBr), berenil, and HOE15030, can be complemented by a wild-type gene with homology to SIR2 of Saccharomyces cerevisiae (ScSIR2). The deduced amino acid sequence of the K. lactis Sir2 prote in has 53% identity with ScSir2 protein but is 108 residues longer. K. lactis sir2 mutants show decreased mating efficiency, deficiency in s porulation, ah increase in recombination at the ribosomal DNA locus, a nd EtBr-induced death. Some functional equivalence between the Sid pro teins of K. lactis and S. cerevisiae has been demonstrated by introduc tion of ScSIR2 into a sir2 mutant of K. lactis. Expression of ScSIR2 o n a multicopy plasmid restores resistance to EtBr and complements spor ulation deficiency. Similarly, mating efficiency of a sir2 mutant of S . cerevisiae is partially restored by K. lactis SIR2 on a multicopy pl asmid. Although these observations suggest that there has been some co nservation of Sid protein function, a striking difference is that sir2 mutants of S. cerevisiae, unlike their K. lactis counterparts, are no t hypersensitive to DNA-targeting drugs.