Crh1p and Crh2p are required for the cross‐linking of chitin to β(1‐6)glucan in the Saccharomyces cerevisiae cell wall

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Abstract
Summary: In budding yeast, chitin is found in three locations: at the primary septum, largely in free form, at the mother‐bud neck, partially linked to β(1‐3)glucan, and in the lateral wall, attached in part to β(1‐6)glucan. By using a recently developed strategy for the study of cell wall cross‐links, we have found that chitin linked to β(1‐6)glucan is diminished in mutants of the CRH1 or the CRH2/UTR2 gene and completely absent in a double mutant. This indicates that Crh1p and Crh2p, homologues of glycosyltransferases, ferry chitin chains from chitin synthase III to β(1‐6)glucan. Deletion of CRH1 and/or CRH2 aggravated the defects of fks1Δ and gas1Δ mutants, which are impaired in cell wall synthesis. A temperature shift from 30°C to 38°C increased the proportion of chitin attached to β(1‐6)glucan. The expression of CRH1, but not that of CRH2, was also higher at 38°C in a manner dependent on the cell integrity pathway. Furthermore, the localization of both Crh1p and Crh2p at the cell cortex, the area where the chitin–β(1‐6)glucan complex is found, was greatly enhanced at 38°C. Crh1p and Crh2p are the first proteins directly implicated in the formation of cross‐links between cell wall components in fungi.
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