Isolation, sequencing, and characterization of crp-5, a gene encoding a Neurospora ribosomal protein

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

Transcription of the ribosomal protein and 40S rRNA genes is coordinately regulated during steady state growth and carbon shifts in Neurospora crassa. Recognition sequences for the Aspergillus nidulans carbon catabolite repressor, CreA, overlap transcriptional elements of a 40S rRNA gene and the crp-2 ribosomal protein gene. They also occur in similar locations in the promoters 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-1 protein is 45% identical to CreA from A. nidulans. Cre-1 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-1 binding specificity from (5'G/CC/TGGG/AG3') to (5'G/CC/TGGCG3'). Base substitutions in the Cre-1 binding sites of the crp-2 promoter disrupted binding of wildtype Cre-1 in vitro but had no effect on transcription during steady state growth or carbon shifts, indicating that regulation of ribosomal genes by carbon source is not mediated by Cre-1, but via different proteins binding the Cre-1 sites and the Dde boxes.

Nutritional and growth control of ribosomal protein mRNA and rRNA in Neurospora crassa

The effects of changing growth rates on the levels of 40S pre-rRNA and two r-protein mRNAs were examined to gain insight into the coordinate transcriptional regulation of ribosomal genes in the ascomycete fungus Neurospora crassa. Growth rates were varied either by altering carbon nutritional conditions, or by subjecting the isolates to inositol-limiting conditions. During carbon up- or down-shifts, r-protein mRNA levels were stoichiometrically coordinated. Changes in 40S pre-rRNA levels paralleled those of the r-protein mRNAs but in a non-stoichiometric manner. Comparison of crp-2 mRNA levels with those of a crp-2::qa-2 fusion gene indicated no major effect from changes in crp-2 mRNA stability. Crp-2 promoter mutagenesis experiments revealed that two elements of the crp-2 promoter, -95 to -83 bp (Dde box) and -74 to -66 bp (CG repeat) important for transcription under constant growth conditions, are also critical for transcriptional regulation by a carbon source. Ribosomal protein mRNA and rRNA levels were unaffected by changes in growth rates when the cultures were grown under inositol-limiting conditions, suggesting that, under these conditions, transcription of the ribosomal genes in N.crassa was regulated independently of growth rate.

Cloning, nucleotide sequence, and expression of tef-1, the gene encoding translation elongation factor 1 alpha (EF-1 alpha) of Neurospora crassa

The tef-1 gene encoding translation elongation factor 1 alpha was cloned from the ascomycete fungus Neurospora crassa. The sequences of genomic DNA and cDNA clones showed that the tef-1 gene contained one ORF of 1380 bp length that is interrupted by three short introns. The deduced polypeptide contained 460 amino acid residues, and the sequence had a high similarity with those of EF-1 alpha polypeptides from other species. The level of tef-1 mRNA was low in conidia but high in growing cells. When mycelia were transferred to poor nutrient media, the level of tef-1 gene mRNA decreased remarkably. The pattern of tef-1 expression was similar to the expression of genes for ribosomal proteins. The tef-1 gene was mapped between arg-3 and leu-4 loci on linkage group I by restriction fragment length polymorphism mapping. Southern blot analysis showed that Neurospora genomic DNA contained only one copy of the tef-1 gene in a genome.

The isolation and characterization of a Neurospora crassa gene (ubi::crp-6) encoding a ubiquitin-40S ribosomal protein fusion protein

We have isolated and sequenced a Neurospora crassa gene encoding a single copy of ubiquitin (UBI) fused to the S27a ribosomal (r) protein. We have opted to name this gene the ubiquitin/cytoplasmic r-protein gene 6 (ubi::crp-6). The ubi::crp-6 gene generates a 700-nucleotide (nt) transcript. It shares a 700-bp regulatory region with the cytoplasmic r-protein gene 5 (crp-5), a gene encoding the N. crassa S26 r-protein. The two genes are transcribed divergently from the common regulatory region and their mRNA levels are regulated in parallel during growth on a variety of carbon sources.