SUPPRESSION OF ESCHERICHIA-COLI ALKB MUTANTS BY SACCHAROMYCES-CEREVISIAE GENES

The alkB gene is one of a group of alkylation-inducible genes in Esche richia coli, and its product protects cells from S(N)2-type alkylating agents such as methyl methanesulfonate (MMS). However, the precise bi ochemical function of the AlkB protein remains unknown. Here, we descr ibe the cloning, sequencing, and characterization of three Saccharomyc es cerevisiae genes (YFW1, YFW12, and YFW16) that functionally complem ent E. call alkB mutant cells. DNA sequence analysis showed that none of the three gene products have a:ny amino acid sequence homology with the AlkB protein. The YFW1 and YFW12 proteins are highly serine and t hreonine rich, and YFW1 contains a stretch of 28 hydrophobic residues, indicating that it may be a membrane protein. The YFW16 gene turned o ut to be allelic with the S. cerevisiae STE11 gene. STE11 is a protein kinase known to be involved in pheromone signal transduction in S. ce revisiae; however, the kinase activity is not required for MMS resista nce because mutant STE11 proteins lacking kinase activity could still complement E. coli alkB mutants. Despite the fact that YFW1, YFW12, an d YFW16/STE11 each confer substantial MMS resistance upon E. coli alkB cells, S. cerevisiae null mutants for each gene were not MMS sensitiv e. Whether these three genes provide alkylation resistance in E. coli via an alkB-like mechanism remains to be determined, but protection ap pears to be specific for AlkB-deficient E. coli because none of the ge nes protect other alkylation-sensitive E. coli strains from killing by MMS.