Carbon regulation of ribosomal genes in Neurospora crassa occurs by a mechanism which does not require Cre-1, the homologue of the Aspergillus carboncatabolite repressor, CreA

Transcription of the ribosomal protein and 40S rRNA genes is coordinately r egulated during steady state growth and carbon shifts in Neurospora crassa, Recognition sequences for the Aspergillus nidulans carbon catabolite repre ssor, CreA, overlap transcriptional elements of a 40S rRNA gene and the crp -2 ribosomal protein gene. They also occur in similar locations in the prom oters of several other ribosomal protein genes. Substitutions encompassing the -74 and -167 CreA consensus sequences in the crp-2 promoter result in a decrease in transcription. A cDNA encoding the N, crassa homologue of CreA was cloned and designated Cre-1,The Cre-l protein is 45% identical to CreA from A. nidulans, Cre-l protein produced in Escherichia coli binds to the CreA sites in the promoters of the 40S rRNA and crp-2 genes. An amino acid change from histidine (92) to threonine changed the Cre-l binding specifici ty from ((5)'(G)/(C)(C)/(T)GG(G)/(A)G(3)') to ((5)'(G)/(C)(C)/(T)GGCG(3)'). Base substitutions in the Cre-l binding sites of the crp-2 promoter disrup ted binding of wildtype Cre-l in vitro but had no effect on transcription d uring steady state growth or carbon shifts, indicating that regulation of r ibosomal genes by carbon source is not mediated by Cre-l, but via different proteins binding the Cre-l sites and the Dde boxes, (C) 1999 Academic Pres s.