The replication-independent histone H3-H4 chaperones HIR, ASF1, and RTT106 co-operate to maintain promoter fidelity.
ABSTRACT RNA polymerase II initiates from low complexity sequences so cells must reliably distinguish "real" from "cryptic" promoters and maintain fidelity to the former. Further, this must be performed under a range of conditions, including those found within inactive and highly transcribed regions. Here, we used genome-scale screening to identify those factors that regulate the use of a specific cryptic promoter and how this is influenced by the degree of transcription over the element. We show that promoter fidelity is most reliant on histone gene transactivators (Spt10, Spt21) and H3-H4 chaperones (Asf1, HIR complex) from the replication-independent deposition pathway. Mutations of Rtt106 that abrogate its interactions with H3-H4 or dsDNA permit extensive cryptic transcription comparable with replication-independent deposition factor deletions. We propose that nucleosome shielding is the primary means to maintain promoter fidelity, and histone replacement is most efficiently mediated in yeast cells by a HIR/Asf1/H3-H4/Rtt106 pathway.
SourceAvailable from: Andrea C Silva[Show abstract] [Hide abstract]
ABSTRACT: Condensin is a central regulator of mitotic genome structure with mutants showing poorly condensed chromosomes and profound segregation defects. Here, we identify NCT, a complex comprising the Nrc1 BET-family tandem bromodomain protein (SPAC631.02), casein kinase II (CKII), and several TAFs, as a regulator of condensin function. We show that NCT and condensin bind similar genomic regions but only briefly colocalize during the periods of chromosome condensation and decondensation. This pattern of NCT binding at the core centromere, the region of maximal condensin enrichment, tracks the abundance of acetylated histone H4, as regulated by the Hat1-Mis16 acetyltransferase complex and recognized by the first Nrc1 bromodomain. Strikingly, mutants in NCT or Hat1-Mis16 restore the formation of segregation-competent chromosomes in cells containing defective condensin. These results are consistent with a model where NCT targets CKII to chromatin in a cell-cycle-directed manner in order to modulate the activity of condensin during chromosome condensation and decondensation.Cell Reports 02/2014; DOI:10.1016/j.celrep.2014.01.029 · 7.21 Impact Factor
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ABSTRACT: Chromatin not only serves as a packaging material, but also functions as a platform for integrating signals that act upon the genome. Indeed, chromatin is a dynamic macromolecular structure that can be dramatically altered in many ways to facilitate the different transactions at the genome. Examples of such alterations are relocalization of genomic loci within the nucleus upon transcriptional activation or induction of DNA damage, adding or removing post-translational modifications on histones or other chromatin-binding factors, or altering the basic organization of chromatin by moving or removing nucleosomes, i.e. modifying the occupancy of histone octamers. New insights into the scope and mechanisms of chromatin dynamics have recently been obtained by the development of novel techniques to visualize chromatin protein mobility and stability. Here we discuss the developments in this area, with special emphasis on histone exchange, which we define as the replacement of histone proteins without a prerequisite change in occupancy. Although histone exchange may not affect chromatin organization per se, recent studies suggest that it can influence key epigenetic processes such as histone inheritance, the distribution of histone post-translational modifications, and the output of transcription factors. Importantly, errors in histone exchange in humans can contribute to malignant transformation.Frontiers in Life Science 06/2013; 7(1-2). DOI:10.1080/21553769.2013.838193 · 0.17 Impact Factor
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ABSTRACT: Chromatin structure in transcribed regions poses a barrier for intragenic transcription. In a comprehensive study of the yeast chromatin remodelers and the Mot1p-NC2 regulators of TATA-binding protein (TBP), we detected synthetic genetic interactions indicative of suppression of intragenic transcription. Conditional depletion of Mot1p or NC2 in absence of the ISW1 remodeler, but not in the absence of other chromatin remodelers, activated the cryptic FLO8 promoter. Likewise, conditional depletion of Mot1p or NC2 in deletion backgrounds of the H3K36 methyltransferase Set2p or the Asf1p-Rtt106p histone H3-H4 chaperones, important factors involved in maintaining a repressive chromatin environment, resulted in increased intragenic FLO8 transcripts. Activity of the cryptic FLO8 promoter is associated with reduced H3 levels, increased TBP binding and tri-methylation of H3K4 and is independent of Spt-Ada-Gcn5-acetyltransferase function. These data reveal cooperation of negative regulation of TBP with specific chromatin regulators to inhibit intragenic transcription.Nucleic Acids Research 01/2014; 42(7). DOI:10.1093/nar/gkt1398 · 8.81 Impact Factor