Transposon mutagenesis reveals novel loci affecting tolerance to salt stress and growth at low temperature

Using transposon mutagenesis in the haploid Saccharomyces cerevisiae strain W303-1A we have identified genes required for growth in high salt medium, survival of a hypo-osmotic shock and growth at 15 degreesC. Screening 25,00 0 transposon insertions revealed a total of 61 insertions that caused salt- sensitivity and those insertions affected 31 genes. Only 12 of those genes were previously known to be required for salt-tolerance. Among the 61 inser tions, three caused general osmo-sensitivity. We identified one single inse rtion mutant in the already-known gene, FPS1, required for survival of hypo -osmotic shock. A total of 31 insertions caused failure to grow at low temp erature. Those identified ten different genes, three of which had previousl y been reported to affect cold-tolerance. Four genes were identified in bot h the salt and the cold-sensitivity screen. We found several unusual insert ion mutations: (1) insertions in or close to essential genes, (2) insertion in an intergenic region and (3) insertions causing stress-sensitivity in W 303-1A, while the deletion mutant in BY4741 did not show such a phenotype. Surprisingly, our mutant set and that reported in the large-scale transposo n insertion project (TRIPLES, http://ygacmed.yale.eud/triples/triples.htm) only marginally overlap. We discuss some of the features of transposon muta genesis in light of the availability of the complete set of yeast deletion mutants and we discuss the possible roles of the genes we identified.