SCREENS FOR EXTRAGENIC MUTATIONS THAT FAIL TO COMPLEMENT ACT1 ALLELESIDENTIFY GENES THAT ARE IMPORTANT FOR ACTIN FUNCTION IN SACCHAROMYCES-CEREVISIAE

Null mutations in SAC6 and ABP1, genes that encode actin-binding prote ins, failed to complement the temperature-sensitive phenotype caused b y a mutation in the ACT1 gene. To identify novel genes whose protein p roducts interact with actin, mutations that fail to complement act1-1 or act1-4, two temperature-sensitive alleles of ACT1, were isolated. A total of 14 extragenic noncomplementing mutations and 12 new alleles of ACT1 were identified in two independent screens. The 14 extragenic noncomplementing mutations represent alleles of at least four differen t genes, ANC1, ANC2, ANC3 and ANC4 (Actin NonComplementing). Mutations in the ANC1 gene were shown to cause osmosensitivity and defects in a ctin organization; phenotypes that are similar to those caused by act1 mutations. We conclude that the ANC1 gene product plays an important role in actin cytoskeletal function. The 12 new alleles of ACT1 will b e useful for further elucidation of the functions of actin in yeast.