Open AccessTFIIIC Binding Sites Function as both Heterochromatin Barriers and Chromatin Insulators in Saccharomyces cerevisiae
Author(s) -
Tiffany A. Simms,
Sandra L. Dugas,
Jason C. Gremillion,
Megan E. Ibos,
M. Nicole Dandurand,
Tasha T. Toliver,
Daniel Edwards,
David Donze
Publication year - 2008
Publication title -
eukaryotic cell
Language(s) - English
Resource type - Journals
eISSN - 1535-9778
pISSN - 1535-9786
DOI - 10.1128/ec.00128-08
Subject(s) - biology , chromatin , heterochromatin , rna polymerase iii , heterochromatin protein 1 , genetics , transcription preinitiation complex , saccharomyces cerevisiae , chromodomain , transcription (linguistics) , rna polymerase ii , microbiology and biotechnology , transcription factor , nucleosome , promoter , gene , rna polymerase , gene expression , rna , helicase , linguistics , philosophy
Chromosomal sites of RNA polymerase III (Pol III) transcription have been demonstrated to have “extratranscriptional” functions, as the assembled Pol III complex can act as chromatin boundaries or pause sites for replication forks, can alter nucleosome positioning or affect transcription of neighboring genes, and can play a role in sister chromatid cohesion. Several studies have demonstrated that assembled Pol III complexes block the propagation of heterochromatin-mediated gene repression. Here we show that inSaccharomyces cerevisiae tRNA genes (tDNAs) and even partially assembled Pol III complexes containing only the transcription factor TFIIIC can exhibit chromatin boundary functions both as heterochromatin barriers and as insulators to gene activation. Both theTRT2 tDNA and theETC4 site which binds only the TFIIIC complex prevented an upstream activation sequence from activating theGAL promoters in our assay system, effectively acting as chromatin insulators. Additionally, when placed downstream from the heterochromaticHMR locus,ETC4 blocked the ectopic spread of Sir protein-mediated silencing, thus functioning as a barrier to repression. Finally, we show thatTRT2 and theETC6 site upstream ofTFC6 in their natural contexts display potential insulator-like functions, andETC6 may represent a novel case of a Pol III factor directly regulating a Pol II promoter. The results are discussed in the context of how the TFIIIC transcription factor complex may function to demarcate chromosomal domains in yeast and possibly in other eukaryotes.