Cloning of the multicopy suppressor gene SUR7: evidence for a functional relationship between the yeast actin-binding protein Rvs167 and a putative membranous protein.

The rvs161 and rvs167 mutant cells exhibit several identical phenotypes including sensitivity to several different growth conditions and morphological defects such as alteration of the actin cytoskeleton and budding patterns. The selection of genes that, when overexpressed, are able to suppress the reduced viability upon carbon starvation of the rvs167 mutant strain, has allowed the cloning of the SUR7 gene (Accession Number Z46729x11). We showed that the suppressive ability of the overexpressed SUR7 gene concerns all the rvs167 phenotypes. However, this suppression is only partial since the rvs167-suppressed strain is not of wild-type phenotype. Moreover, SUR7 is also able to suppress partially the phenotypes exhibited by the rvs161 and rvs167 and rvs161 mutant strains. The SUR7 gene encodes a putative integral membrane protein with four transmembrane domains. Furthermore, sequence comparisons revealed that Sur7p and two other proteins, Yn1194p and Yd1222p, present significant sequence and structural similarities. Taken together, these results strongly suggest that the Rvs161 and Rvs167 proteins act together in relation with Sur7p. Moreover, the putative transmembranous character of Sur7p suggests a membrane localization of the Rvs function, a localization which is consistent with the different rvs phenotypes and the actin-Rvs167p interaction.