A CBF5 mutation that disrupts nucleolar localization of early tRNA biosynthesis in yeast also suppresses tRNA gene-mediated transcriptional silencing.
In the budding yeast, Saccharomyces cerevisiae, actively transcribed tRNA genes can negatively regulate adjacent RNA polymerase II (pol II)-transcribed promoters. This tRNA gene-mediated silencing is independent of the orientation of the tRNA gene and does not require direct, steric interference with the binding of either upstream pol II factors or the pol II holoenzyme. A mutant was isolated in which this form of silencing is suppressed. The responsible point mutation affects expression of the Cbf5 protein, a small nucleolar ribonucleoprotein protein required for correct processing of rRNA. Because some early steps in the S. cerevisiae pre-tRNA biosynthetic pathway are nucleolar, we examined whether the CBF5 mutation might affect this localization. Nucleoli were slightly fragmented, and the pre-tRNAs went from their normal, mostly nucleolar location to being dispersed in the nucleoplasm. A possible mechanism for tRNA gene-mediated silencing is suggested in which subnuclear localization of tRNA genes antagonizes transcription of nearby genes by pol II.
Kendall
A
A
Department of Biological Chemistry and Program in Cellular and Molecular Biology, University of Michigan, Ann Arbor, MI 48109-0606, USA.
Hull
M W
MW
Bertrand
E
E
Good
P D
PD
Singer
R H
RH
Engelke
D R
DR
D002466:Cell Nucleolus / Q000502:physiology*; D003001:Cloning, Molecular; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal / Q000502:physiology*; D020868:Gene Silencing; D006836:Hydro-Lyases / Q000235:genetics; D008869:Microtubule-Associated Proteins / Q000235:genetics* / Q000378:metabolism*; D017354:Point Mutation; D011401:Promoter Regions, Genetic; D012319:RNA Polymerase II / Q000378:metabolism; D012322:RNA Precursors / Q000096:biosynthesis / Q000235:genetics; D012331:RNA, Fungal / Q000096:biosynthesis / Q000235:genetics; D012343:RNA, Transfer / Q000096:biosynthesis* / Q000235:genetics*; D016601:RNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D014158:Transcription, Genetic
D005656:Fungal Proteins; D008869:Microtubule-Associated Proteins; D012322:RNA Precursors; D012331:RNA, Fungal; D016601:RNA-Binding Proteins; D017411:Ribonucleoproteins, Small Nuclear; D029701:Saccharomyces cerevisiae Proteins; D012343:RNA, Transfer; D012319:RNA Polymerase II; D006836:Hydro-Lyases; C021434:imidazoleglycerolphosphate dehydratase; C082278:CBF5 protein, S cerevisiae