title: The yeast nucleolar protein Cbf5p is involved in rRNA biosynthesis and interacts genetically with the RNA polymerase I transcription factor RRN3.
abstract: Yeast Cbf5p was originally isolated as a low-affinity centromeric DNA binding protein (W. Jiang, K. Middleton, H.-J. Yoon, C. Fouquet, and J. Carbon, Mol. Cell. Biol. 13:4884-4893, 1993). Cbf5p also binds microtubules in vitro and interacts genetically with two known centromere-related protein genes (NDC10/CBF2 and MCK1). However, Cbf5p was found to be nucleolar and is highly homologous to the rat nucleolar protein NAP57, which coimmunoprecipitates with Nopp140 and which is postulated to be involved in nucleolar-cytoplasmic shuttling (U. T. Meier, and G. Blobel, J. Cell Biol. 127:1505-1514, 1994). The temperature-sensitive cbf5-1 mutant demonstrates a pronounced defect in rRNA biosynthesis at restrictive temperatures, while tRNA transcription and pre-rRNA and pre-tRNA cleavage processing appear normal. The cbf5-1 mutant cells are deficient in cytoplasmic ribosomal subunits at both permissive and restrictive temperatures. A high-copy-number yeast genomic library was screened for genes that suppress the cbf5-1 temperature-sensitive growth phenotype. SYC1 (suppressor of yeast cbf5-1) was identified as a multicopy suppressor of cbf5-1 and subsequently was found to be identical to RRN3, an RNA polymerase I transcription factor. A cbf5delta null mutant is not rescued by plasmid pNOY103 containing a yeast 35S rRNA gene under the control of a Pol II promoter, indicating that Cbf5p has one or more essential functions in addition to its role in rRNA transcription.
authors.affiliation: Department of Molecular, Cellular, and Developmental Biology, University of California, Santa Barbara 93106, USA.
authors.forename: C
authors.initials: C
authors.lastname: Cadwell
authors.forename: H J
authors.initials: HJ
authors.lastname: Yoon
authors.forename: Y
authors.initials: Y
authors.lastname: Zebarjadian
authors.forename: J
authors.initials: J
authors.lastname: Carbon
mesh_terms: D003593:Cytoplasm / Q000737:chemistry; D005656:Fungal Proteins / Q000235:genetics / Q000502:physiology*; D005800:Genes, Fungal / Q000235:genetics; D016153:Genes, Suppressor / Q000235:genetics; D006836:Hydro-Lyases; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000502:physiology*; D009154:Mutation; D035463:Pol1 Transcription Initiation Complex Proteins; D012318:RNA Polymerase I; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000096:biosynthesis*; D012335:RNA, Ribosomal / Q000096:biosynthesis* / Q000378:metabolism; D012343:RNA, Transfer / Q000096:biosynthesis; D015183:Restriction Mapping; D017411:Ribonucleoproteins, Small Nuclear; D012270:Ribosomes / Q000737:chemistry; D012441:Saccharomyces cerevisiae / Q000201:enzymology / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D013696:Temperature; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*; D014158:Transcription, Genetic / Q000502:physiology
chemical_list: D005656:Fungal Proteins; D008869:Microtubule-Associated Proteins; D035463:Pol1 Transcription Initiation Complex Proteins; D012331:RNA, Fungal; D012335:RNA, Ribosomal; C101161:RRN3 protein, S cerevisiae; D017411:Ribonucleoproteins, Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D012343:RNA, Transfer; D012318:RNA Polymerase I; D006836:Hydro-Lyases; C082278:CBF5 protein, S cerevisiae