Summary: The gene, originally isolated by complementation of a K9 killer-toxin-resistant mutant displaying reduced levels of both 1,3-β-glucan and 1,3-β-glucan synthase activity, was recloned from a YCp50 genomic library as a suppressor of calcofluor-white-hypersensitive () mutants. In these mutants, which were characterized by increased chitin levels, the suppressor effect of resulted, for some of them, in a lowering of polymer content to close to wild-type level, with no effect on the contents of β-glucan and mannan. In all cases, this effect was accompanied by a strong reduction in mRNA levels corresponding to and encoding chitin synthases, without affecting expression of and two genes encoding the catalytic subunit and a regulatory component of 1,3-β-glucan synthase, respectively. Overexpression of also inhibited expression of genes in wild-type strains and in two other mutants, whose sensitivity to calcofluor white was not suppressed by this gene. The physiological relevance of the transcriptional effect was addressed in two different ways. In a wild-type strain exposed to α-factor, overexpression of this gene inhibited induction and delayed shmoo formation, two events which are triggered in response to the pheromone, whereas it did not affect bud formation and cell growth in a double mutant. A chimeric protein made by fusing green fluorescent protein to the C terminus of Knr4p which fully complemented a Δ mutation was found to localize in patches at presumptive bud sites in unbudded cells and at the incipient bud site during bud emergence. Taken together, these results demonstrate that has a regulatory role in chitin deposition and in cell wall assembly. A mechanism by which this gene affects expression of genes is proposed.


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