In Schizosaccharomyces pombe, Bgs1/Cps1p is a (1,3)-glucan synthase required for linear
(1,3)-glucan synthesis and primary septum formation. Here, we have studied the regulation of Bgs1p by Cfh3/Chr4p, a member of a family of conserved adaptor proteins, which resembles the chitin synthase regulator Chs4p from Saccharomyces cerevisiae and Candida albicans. cfh3 cells showed a genetic interaction with cps1-191, and Cfh3p co-immunoprecipitated with Bgs1/Cps1p. In the absence of cfh3, cells were more sensitive to digestion by glucanases, and both Calcofluor staining and glucan synthesis were reduced. We found that in a wild-type strain,
(1,3)-glucan synthesis was reduced under stress conditions. In the cfh3, cps1-191, and cfh3 cps1-191 strains,
(1,3)-glucan synthesis was further reduced, and growth was impaired under stress conditions, suggesting that Cfh3p and Bgs1p might play a role in ensuring growth in unfavorable environments. In a cfh3 mutant, Bgs1p was delocalized when the cells were distressed, but a blockade in endocytosis prevented this delocalization. Finally, we found that the SEL1 repeats are required for Cfh3p function. These results show that Cfh3p is a regulatory protein for Bgs1p and that its function is particularly necessary when the cells are undergoing stress.

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