TRANSCRIPTIONAL ACTIVATION OF A CYCLOHEXIMIDE-INDUCIBLE GENE ENCODINGLACCASE IS MEDIATED BY CPC-1, THE CROSS-PATHWAY CONTROL GENE, IN NEUROSPORA-CRASSA

Expression of the laccase gene (lace) of Neurospora crassa is transcri ptionally inducible by the protein synthesis inhibitor cycloheximide. A lni-1 mutation, conferring the laccase non-inducible phenotype, was found to be a cpc-1 allele. Northern blots probed with plasmid pLA1, w hich carries the lacc gene revealed that the cpc-1 mutation abolishes the induced transcription of the lace gene, indicating requirement of the cpc-1 gene for transcriptional activation of the lace gene. In Nor thern blots probed with plasmid pAB1, which bears arg-2 a gene whose t ranscription is under the control of CPC1, the level of the arg-a tran script was shown to increase several-fold in wild-type mycelia but rem ained low in cpc-1 mycelia, after treatment with cycloheximide. This s uggests that inhibition of protein synthesis with cycloheximide, as we ll as amino acid limitation, elicits the CPC1-mediated cross-pathway c ontrol. Characterization of the lace upstream region using a series of 5'-deletion plasmids led to the identification of a 170 bp DNA region required for the induced lace expression. Sequence analysis of this D NA region demonstrated that it includes a 9 bp sequence with dyad symm etry, ATGAATCAT, which differs only by a central base pair from ATGA(C /G)TCAT, the recognition sequence characteristic of CPC1 and GCN4 bind ing sites. Possible mechanisms by which CPC1 mediates transcriptional activation of the lace gene are discussed.