CPC-3, THE NEUROSPORA-CRASSA HOMOLOG OF YEAST GCN2, ENCODES A POLYPEPTIDE WITH JUXTAPOSED EIF2-ALPHA KINASE AND HISTIDYL-TRANSFER-RNA SYNTHETASE-RELATED DOMAINS REQUIRED FOR GENERAL AMINO-ACID CONTROL

Based on characteristic amino acid sequences of kinases that phosphory late the alpha subunit of eukaryotic translation initiation factor 2 ( eIF2 alpha kinases), degenerate oligonucleotide primers were construct ed and used to polymerase chain reaction-amplify from genomic DNA of N eurospora crassa a sequence encoding part of a putative protein kinase . With this sequence an open reading frame was identified encoding a p redicted polypeptide with juxtaposed eIF2 alpha kinase and histidyl-tR NA synthetase-related domains. The 1646 amino acid sequence of this ge ne, called cpc-3, showed 35% positional identity over almost the entir e sequence with GCN2 of yeast, which stimulates translation of the tra nscriptional activator of amino acid biosynthetic genes encoded by GCN 4, Strains disrupted for cpc-3 were unable to induce increased transcr iption and derepression of amino acid biosynthetic enzymes in amino ac id-deprived cells. The cpc-3 mutation did not affect the ability to up -regulate mRNA levels of cpc-1, encoding the GCN4 homologue and transc riptional activator of amino acid biosynthetic genes in N. crassa, but the mutation abolished the dramatic increase of CPC1 protein level in response to amino acid deprivation, These findings suggest that cpc-3 is the functional homologue of GCN2, being required for increased tra nslation of cpc-1 mRNA in amino acid-starved cells.