We isolated a temperature-sensitive mutant of Saccharomyces cerevisiae in which transcription both of ribosomal protein genes and of ribosomal RNA is defective at the non-permissive temperature. Temperature-sensitivity for growth is recessive and segregates 2:2. The wild type gene, termed RIC1 (for ribosome control) was cloned by complementation of the temperature-sensitive phenotype from a genomic DNA library based on the CEN plasmid. RIC1 encodes a protein of 1056 amino acid (aa) residues including a putative nuclear localization sequence. Data base searches revealed that RIC1 is a novel gene and predicted aa sequence share some sequence similarity with viral transcriptional regulatory proteins.