title: Requirement of Nhp6 proteins for transcription of a subset of tRNA genes and heterochromatin barrier function in Saccharomyces cerevisiae.
abstract: A key event in tRNA gene (tDNA) transcription by RNA polymerase (Pol) III is the TFIIIC-dependent assembly of TFIIIB upstream of the transcription start site. Different tDNA upstream sequences bind TFIIIB with different affinities, thereby modulating tDNA transcription. We found that in the absence of Nhp6 proteins, the influence of the 5'-flanking region on tRNA gene transcription is dramatically enhanced in Saccharomyces cerevisiae. Expression of a tDNA bearing a suboptimal TFIIIB binding site, but not of a tDNA preceded by a strong TFIIIB binding region, was strongly dependent on Nhp6 in vivo. Upstream sequence-dependent stimulation of tRNA gene transcription by Nhp6 could be reproduced in vitro, and Nhp6 proteins were found associated with tRNA genes in yeast cells. We also show that both transcription and silencing barrier activity of a tDNA(Thr) at the HMR locus are compromised in the absence of Nhp6. Our data suggest that Nhp6 proteins are important components of Pol III chromatin templates that contribute both to the robustness of tRNA gene expression and to positional effects of Pol III transcription complexes.
authors.affiliation: Dipartimento di Biochimica e Biologia Molecolare, Università degli Studi di Parma, Viale G.P. Usberti 23A, 43100 Parma, Italy.
authors.forename: Priscilla
authors.initials: P
authors.lastname: Braglia
authors.forename: Sandra L
authors.initials: SL
authors.lastname: Dugas
authors.forename: David
authors.initials: D
authors.lastname: Donze
authors.forename: Giorgio
authors.initials: G
authors.lastname: Dieci
mesh_terms: D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D024001:HMGN Proteins; D006570:Heterochromatin / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012320:RNA Polymerase III / Q000378:metabolism; D012331:RNA, Fungal / Q000235:genetics; D012343:RNA, Transfer / Q000235:genetics*; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D035361:Transcription Factor TFIIIB / Q000378:metabolism; D019474:Transcription Factors, TFIII; D014158:Transcription, Genetic / Q000235:genetics*; D000098832:Transcription Factor TFIIIC
chemical_list: D004268:DNA-Binding Proteins; D024001:HMGN Proteins; D006570:Heterochromatin; C086471:NHP6A protein, S cerevisiae; C086472:NHP6B protein, S cerevisiae; D009687:Nuclear Proteins; D012331:RNA, Fungal; D011994:Recombinant Proteins; D029701:Saccharomyces cerevisiae Proteins; D035361:Transcription Factor TFIIIB; D019474:Transcription Factors, TFIII; D000098832:Transcription Factor TFIIIC; D012343:RNA, Transfer; D012320:RNA Polymerase III