The frost gene of Neurospora crassa is a homolog of yeast cdc1 and affectshyphal branching via manganese homeostasis

The Neurospora crassa mutant frost has a hyperbranching phenotype that can be corrected by adding Ca2+, suggesting that characterization of this gene might clarify the mechanism of Ca2+-dependent tip growth. The wild-type all ele was cloned by sib selection using protoplasts from arthroconidia, RFLP analysis revealed that the cloned DNA fragment mapped to the fu locus. The nucleotide sequence of genomic and cDNA was determined. The deduced amino a cid sequence showed homology to the Saccharomyces cerevisiae CDCl protein, implicated in manganese homeostasis, The fr mutant was sensitive to Mn2+, a nd a revertant allele whose product differs by one amino acid was tolerant to Mn2+. Mn2+ depletion induced the wild-type strain to hyperbranch, result ing in a morphology similar to that of fr. The fr mutant was also sensitive to calcineurin inhibitors. These results suggest that fr is involved in Mn 2+ homeostasis and point to a role for Mn2+ in Neurospora branching. (C) 19 99 Academic Press.