Project description:Asf1, through its histone chaperone activity, helps chromatin closing/opening during DNA replication, repair, recombination and transcription. Despite extensive research on Asf1-mediated physiological functions, a genome-wide localization map is lacking, limiting our knowledge of chromosomal features targeted by Asf1. We present a high-resolution genome-wide map of Asf1, localizing at essentially all pol III-transcribed genes, highly active pol II-transcribed genes and heterochromatic features. Pol III-transcribed genes are negatively regulated by Asf1, whereas pol II genes are regulated indirectly by Asf1-dependent H3K56 acetylation. Interestingly, Asf1 localization along yeast chromosomes shows nearly identical distribution to that of the condensin complex, predicting a functional overlap in chromosome architecture and genome organization. ChIP-seq analysis of Asf1 targets using a yeast strain that expresses an 18-Myc tag fused to the C-terminus of ASF1. Two biological replicates and one mock/control were performed. The Illumina GAII was used. ChIP-seq reads are aligned to the budding yeast sacCer3 (2011) assembly.
Project description:Genome-wide distribtuion of histone H3K56ac (histone H3 acetylated at lysine 56) was analyzed in the wild type and the sterile mutant asf1. The asf1 gene encodes a conserved histone chaperone, and preliminary experimentes indicated changes in histone modifications in the mutant that were analyzed on a genome-wide basis in these experiments.
Project description:Genome-wide distribtuion of histone H3 and H3K27me3 (histone H3 tri-methylated at lysine 27) was analyzed in the wild type and the sterile mutant asf1. The asf1 gene encodes a conserved histone chaperone, and preliminary experimentes indicated changes in histone modifications in the mutant that were analyzed on a genome-wide basis in these experiments.
Project description:Asf1, through its histone chaperone activity, helps chromatin closing/opening during DNA replication, repair, recombination and transcription. Despite extensive research on Asf1-mediated physiological functions, a genome-wide localization map is lacking, limiting our knowledge of chromosomal features targeted by Asf1. We present a high-resolution genome-wide map of Asf1, localizing at essentially all pol III-transcribed genes, highly active pol II-transcribed genes and heterochromatic features. Pol III-transcribed genes are negatively regulated by Asf1, whereas pol II genes are regulated indirectly by Asf1-dependent H3K56 acetylation. Interestingly, Asf1 localization along yeast chromosomes shows nearly identical distribution to that of the condensin complex, predicting a functional overlap in chromosome architecture and genome organization.
Project description:Histones are the protein components of the basic unit of chromatin, the core particle of the nucleosome. They play a central role in defining chromatin states associated with distinct cell fates and are classified into replicative and non-replicative/replacement histone variants. While the latter do not exhibit S phase regulation in their expression, the replicative histone variants show a major peak in expression early during S phase to support chromatin assembly during replication of the genome. Their expression is tightly regulated during the cell-cycle both transcriptionally and post-transcriptionally and involves a number of actors. During replication in human cells, two main chaperones ensure the deposition of H3-H4 onto DNA: Chromatin assembly factor 1 (CAF-1) and Anti-silencing factor 1 (ASF1). Interestingly, on the one hand, ASF1 binds the newly synthesized replicative histones H3.1/H3.2-H4 to hand them off to the downstream chaperone, CAF-1, for deposition onto the duplicated DNA strands in a DNA synthesis-coupled (DSC) manner. On the other hand, ASF1 also promotes the recycling of parental histones during replication. In addition, ASF1 binds the non-replicative variant H3.3 and hands it off to the downstream chaperone Histone regulator A (HIRA) for deposition of H3.3 in a DNA synthesis independent (DSI) manner. Finally, in human cells, ASF1 but not CAF-1, also provides a buffering system for histone excess generated in response to stalled replication, indicating yet another role for ASF1 in regulating the flow of replicative histones in higher eukaryotes. However, to date, roles of these chaperones in histone RNA metabolism in mammals had remained unexplored. This is particularly interesting to consider given that in budding yeast, where there are no distinct replicative and non-replicative H3 variants, the single ASF1 ortholog participates in activating transcription of histone genes in S phase and transcriptional repression outside S phase in combination with Hir1, the budding yeast counterpart of HIRA. We thus decided to explore how the key histone chaperones involved in DNA synthesis-coupled chromatin assembly could contribute to the critical regulation of expression of replicative histone genes in human cells during S phase. From total RNA extracted from asynchronous and synchronized human cells, we performed RNA-seq and found that most of the annotated replicative histone genes decreased in expression upon ASF1 depletion by siRNA during S phase compared to the control condition with siRNA againt GFP. However, by 4sU-labeled RNA-seq we detected an increase in newly synthesized replicative histone transcripts. These findings indicate that the decrease in expression of replicative histone genes in ASF1-depleted cells cannot be due to a decrease at the level of transcription. We then inspected closely the sequences at the 3’ end of the replicative histone transcripts in our RNA-seq data and detected a defect of their 3’ processing. Thus, we propose that in mammals ASF1 plays a role in the unique regulation of replicative histone RNA metabolism.
Project description:Histone chaperones and chromatin remodelers control nucleosome dynamics, which are essential for transcription, replication, and DNA repair. The histone chaperone Anti-Silencing Factor 1 (ASF1) plays a central role in facilitating CAF-1-mediated replication-dependent H3.1 deposition and HIRA-mediated replication-independent H3.3 deposition in yeast and metazoans. Whether ASF1 function is evolutionarily conserved in plants is unknown. Here, we show that Arabidopsis ASF1 proteins display a preference for the HIRA complex. Simultaneous mutation of both Arabidopsis ASF1 genes caused a decrease in chromatin density and ectopic H3.1 occupancy at loci typically enriched with H3.3. Genetic, transcriptomic, and proteomic data indicate that ASF1 proteins strongly prefers the HIRA complex over CAF-1. asf1 mutants also displayed an increase in spurious Pol II transcriptional initiation and showed defects in the maintenance of gene body CG DNA methylation and in the distribution of histone modifications. Furthermore, ectopic targeting of ASF1 caused excessive histone deposition, less accessible chromatin, and gene silencing. These findings reveal the importance of ASF1-mediated histone deposition for proper epigenetic regulation of the genome.
Project description:The evolutionarily conserved HIRA/Hir histone chaperone complex and ASF1/Asf1 co-chaperone cooperate for replication-independent chromatin assembly. Here we report the molecular architecture of the Hir complex with Asf1/H3/H4 via single-particle cryo-EM and crosslinking mass spectrometry.