A PBS2 homologue from Debaryomyces hansenii shows a differential effect on calcofluor and polymyxin B sensitivity in Saccharomyces cerevisiae.

The PBS2 gene encodes a MAP kinase kinase that plays a pivotal role in osmosensing signal-transduction pathway in the yeast Saccharomyces cerevisiae. Mutation in the PBS2 gene has a pleotropic effect. Besides being osmosensitive, pbs2 mutants show altered sensitivity to polymyxin B and calcofluor. Recent studies revealed that Pbs2p plays a different role in osmoadaptation and calcofluor sensitivity. We have isolated a gene homologous to PBS2 from the highly salt-tolerant yeast Debaryomyces hansenii by phenotypic complementation. DNA sequencing of the clone revealed that the gene encoded a protein of 683 amino acid residues. Like Pbs2p, this protein also has a proline-rich motif. Further characterization revealed that this gene could complement polymyxin B sensitivity but did not affect calcofluor sensitivity. Thus, it appeared that Pbs2p also has an independent role in these two physiological processes. The GenBank Accession No. of this sequence is AF371315.