CHARACTERIZATION OF THE YEAST (1-]6)-BETA-GLUCAN BIOSYNTHETIC COMPONENTS, KRE6P AND SKN1P, AND GENETIC INTERACTIONS BETWEEN THE PKCI PATHWAY AND EXTRACELLULAR-MATRIX ASSEMBLY

A characterization of the S. cerevisiae KRE6 and SKN1 gene products ex tends previous genetic studies on their role in (1-->6)-beta-glucan bi osynthesis (Roemer, T., and H. Bussey. 1991. Yeast beta-glucan synthes is: KRE6 encodes a predicted type II membrane protein required for glu can synthesis in vivo and for glucan synthase activity in vitro. Proc. Natl., Acad. Sci. USA. 88:11295-11299; Roemer, T., S. Delaney, and H. Bussey. 1993. SKN1 and KRE6 define a pair of functional homologs enco ding putative membrane proteins involved in beta-glucan synthesis. Mol . Cell. Biol. 13:4039-4048). KRE6 and SKN1 are predicted to encode hom ologous proteins that participate in assembly of the cell wall polymer (1-->6)-beta-glucan. KRE6 and SKN1 encode phosphorylated integral-mem brane glycoproteins, with Kre6p likely localized within a Golgi subcom partment. Deletion of both these genes is shown to result in a dramati c disorganization of cell wall ultrastructure. Consistent with their d irect role in the assembly of this polymer, both Kre6p and Skn1p posse ss COOH-terminal domains with significant sequence similarity to two r ecently identified glucan-binding proteins. Deletion of the yeast prot ein kinase C homolog, PKC1, leads to a lysis defect (Levin, D. E., and E. Bartlett-Heubusch. 1992. Mutants in the S. cerevisiae PKC1 gene di splay a cell cycle-specific osmotic stability defect. J. Cell Biol. 11 6:1221-1229). Kre6p when even mildly overproduced, can suppress this p kc1 lysis defect. When mutated, several KRE pathway genes and members of the PKC1-mediated MAP kinase pathway have synthetic lethal interact ions as double mutants. These suppression and synthetic lethal interac tions, as well as reduced P-glucan and mannan levels in the pkc1 null wall, support a role for the PKC1 pathway functioning in cell wall ass embly. PKC1 potentially participates in cell wall assembly by regulati ng the synthesis of cell wail components, including (1-->6)-beta-gluca n.