EXTRAGENIC SUPPRESSORS OF NUDC3, A MUTATION THAT BLOCKS NUCLEAR MIGRATION IN ASPERGILLUS-NIDULANS

Nuclear migration plays an important role in the growth and developmen t of many organisms including the filamentous fungus Aspergillus nidul ans. We have cloned three genes from A. nidulans, nudA, nudC, and nudF , in which mutations affect nuclear migration. The nudA gene encodes t he heavy chain of cytoplasmic dynein. The nudC gene encodes a 22-kD pr otein. The nudF gene was identified as an extracopy suppressor of the temperature sensitive (ts(-)) nudC3 mutation. The nudC3 mutation subst antially decreases the intracellular concentration of the nudF protein at restrictive temperature. This is restored toward the normal level by an extra copy of nudF. To identify other genes whose products inter act directly or indirectly with the NUDC protein, we have isolated a s et of extragenic suppressors of the nudC3 temperature-sensitive mutati on. Genetic analysis of 16 such extragenic suppressors showed them to represent nine different genes, designated sncA-sncI (for (s) under ba r uppressor of (n) under bar ud (C) under bar). sncA-sncH were either dominant or semidominant in diploids homozygous for nudC3 and heterozy gous for the snc mutations. All of the suppressors reversed the ts(-) phenotype of nudC3 by restoring the intracellular concentration of the NUDF protein.