YEAST KRE GENES PROVIDE EVIDENCE FOR A PATHWAY OF CELL-WALL BETA-GLUCAN ASSEMBLY

The Saccharomyces cerevisiae KRE1 gene encodes a Ser/Thr-rich protein, that is directed into the yeast secretory pathway, where it is highly modified, probably through addition of O-linked mannose residues. Gene disruption of the KRE1 locus leads to a 40% reduced level of cell wall (1→6)-β-glucan. Structural analysis of the (1→6)-β-glucan fraction, isolated from a strain with a krel disruption mutation, showed that it had an altered structure with a smaller average polymer size. Mutations in two other loci, KRE5 and KRE6 also lead to a defect in cell wall (1→6)-β-glucan production and appear to be epistatic to KRE1. These findings outline a possible pathway of assembly of yeast cell wall (1→6)-β-glucan.