SRD1, A SACCHAROMYCES-CEREVISIAE GENE AFFECTING PRE-RIBOSOMAL-RNA PROCESSING CONTAINS A C-2 C-2 ZINC-FINGER MOTIF/

The Saccharomyces cerevisiae genes, RRP1 and SRD1, are involved in pro cessing rRNA precursor species to mature rRNAs. We reported previously that the rrp1-1 mutation caused temperature-sensitive lethality, hype rsensitivity to aminoglycoside antibiotics, and defective processing o f 27S pre-rRNA to 25S and 5.8S mature rRNAs. A second-site suppressor of the rrp1-1 mutation, srd1, corrects all three rrp1 mutant phenotype s. In order to learn more about the roles of the SRD1 and RRP1 genes i n rRNA processing, we cloned and characterized the SRD1 gene. We ident ified an ORF, YCR18C, that complements srd1-2 suppression of rrp1-1. T he DNA is physically located at the region of chromosome III where SRD 1 has been genetically mapped. SRD1 encodes a putative 225 amino acid, 26 kDa protein containing a C-2/C-2 zinc finger motif that is also fo und in some transcription regulators and the elF-2 beta translation in itiating factors. The similarity of SRD1 to transcription regulators l ed us to test the model that srd1 mutations suppress rrp1 defects by a ltering the level of the RRP1 transcript. However, we found that SRD1 has no detectable effect on the steady state levels of RRP1 mRNA. We d escribe alternative models to explain the role of Srd1p in pre-rRNA pr ocessing.