Screening and characterization of transposon-insertion mutants in a pseudohyphal strain of Saccharomyces cerevisiae.

Strains of Saccharomyces cerevisiae with sigma1278b background are widely used for elucidation of pseudohyphal differentiation and signal transduction. However, information and resources on the strains are limited compared to the S288C strains. To facilitate functional analysis of strains with sigma1278b background, mutant strains were generated by using a mini-transposon3-3 x HA/LacZ (mTn3)-mutagenized library. Mutants with mTn3 insertions were screened for expression of beta-galactosidase activity under nitrogen starvation and the insertion sites were identified. One hundred and five heterozygous diploid strains were selected and subjected to tetrad analysis. Insertion of mTn3 in 11 genes was lethal in the strain, including three genes, HAC1, TPS1 and UME6, which are non-essential genes according to the Saccharomyces Genome Database. Viable haploid strains with mTn3 insertions were examined for invasive growth, which is a differentiation process in haploid strains including agar penetration on rich medium, and cell morphology during invasive growth. We also examined homozygous diploid strains with mTn3-insertions for filamentous growth and sporulation.