The relative levels of rRNAs and ribosomal proteins are coordinately regulated by growth rate and carbon nutrition in Neurospora crassa. However, little is known about the mechanisms involved. To investigate the transcriptional regulation of ribosomal protein genes in N. crassa, we cloned and sequenced a ribosomal protein gene (crp-3). The inferred crp-3 protein sequence shares 89% and 83% homology at its N-terminus with the yeast rp51 and the human S17 ribosomal proteins respectively. The crp-3 gene contains two introns, neither of which are conserved in position with the RP51 or the S17 genes. The crp-3 gene is present in a single copy and was mapped by RFLP analysis to the right arm of linkage group IV, near the cot-1 locus. Sequence comparisons of the upstream regions of the three sequenced crp genes revealed several common features. These include a 'Taq box' (consensus: ARTTYGACTT) at -39, a CG repeat (consensus: CCCRCCRRR) at -65, and a major transcription initiation site embedded in a purine rich region flanked by an upstream pyrimidine rich sequence. Using four N.crassa ribosomal protein genes as probes, we demonstrated that the levels of the four ribosomal protein mRNAs were closely coordinated during a nutritional downshift from sucrose to quinic acid.