Cytochalasin-E-Resistant Mutants of Coprinus cinereus: Isolation and Genetic, Biochemical, and Cytological Analyses

We first obtained a cytochalasin-E supersensitive strain (CES14) of the basidiomycete Coprinus cinereus and then isolated 1000 revertants of CES14, expecting that at least some of the revertants have defects in the functions of actin filaments. Microscopic examination revealed that three of the revertants lack septa in their hyphae. Of the 1000 revertants, 18 including the 3 septumless strains were genetically analyzed. In 11 of the 18 revertants, reversion was due to extragenic suppressor mutations of ces14. Ten of the 11 mutations were in the same locus designated cer1, while the locus of the remaining mutation, which inhibits septum formation, could not be determined because of its failure to mate with any other cer1 strains. In one (CES14R42) of the cer1 mutants, actin appeared to be altered in the affinity to actin antibody in Western blotting after isoelectric focusing, suggesting that cer1 is a gene encoding actin. Phenotypic examination revealed that the 10 cer1 mutations all confer resistance to cytochalasin-E and that two of the cer1 mutations, both of which block septation, inhibit the formation of the actin ring.