THE CPC-2 GENE OF NEUROSPORA-CRASSA ENCODES A PROTEIN ENTIRELY COMPOSED OF WD-REPEAT SEGMENTS THAT IS INVOLVED IN GENERAL AMINO-ACID CONTROL AND FEMALE FERTILITY

Phenotypic and molecular studies of the mutation U142 indicate that th e cpc-2(+) gene is required to activate general amino acid control und er conditions of amino acid limitation in the vegetative growth phase, and for formation of protoperithecia in preparation for the sexual ph ase of the life cycle of Neurospora crassa. The cpc-2 gene was cloned by complementation of the cpc-2 mutation in a his-2(ts) bradytrophic b ackground. Genomic and cDNA sequence analysis indicated a 1636 bp long open reading frame interrupted by four introns. The deduced 316 amino acid polypeptide reveals 70% positional identity over its full length with G-protein beta-subunit-related polypeptides found in humans, rat (RACK1), chicken, tobacco and Chlamydomonas. With the exception of RA CK1 the function of these proteins is obscure. All are entirely made u p of seven WD-repeats. Expression studies of cpc-2 revealed one abunda nt transcript in the wild type; in the mutant its level is drastically reduced. In mutant cells transformed with the complementing sequence, the transcript level, enzyme regulation and female fertility are rest ored. In the wild type the cpc-2 transcript is down-regulated under co nditions of amino acid limitation. With cpc-2 a new element involved i n general amino acid control has been identified, indicating a functio n for a WD-repeat protein that belongs to a class that is conserved th roughout the evolution of eukaryotes.