Establishment and Maintenance of Chromatin Architecture Are Promoted Independently of Transcription by the Histone Chaperone FACT and H3-K56 Acetylation in Saccharomyces cerevisiae

Abstract

FACT (FAcilitates Chromatin Transcription/Transactions) is a histone chaperone that can destabilize or assemble nucleosomes. Acetylation of histone H3-K56 weakens a histone-DNA contact that is central to FACT activity, suggesting that this modification could affect FACT functions. We tested this by asking how mutations of H3-K56 and FACT affect nucleosome reorganization activity in vitro, and chromatin integrity and transcript output in vivo. Mimics of unacetylated or permanently acetylated H3-K56 had different effects on FACT activity as expected, but the same mutations had surprisingly similar effects on global transcript levels. The results are consistent with emerging models that emphasize FACT's importance in establishing global chromatin architecture prior to transcription, promoting transitions among different states as transcription profiles change, and restoring chromatin integrity after it is disturbed. Optimal FACT activity required the availability of both modified and unmodified states of H3-K56. Perturbing this balance was especially detrimental for maintaining repression of genes with high nucleosome occupancy over their promoters and for blocking antisense transcription at the +1 nucleosome. The results reveal a complex collaboration between H3-K56 modification status and multiple FACT functions, and support roles for nucleosome reorganization by FACT before, during, and after transcription.

FACT and Ash1 promote long-range and bidirectional nucleosome eviction at the HO promoter

“…Blue, red and green lines indicate relative nucleosome enrichment as determined by H3 ChIP after 0, 20 and 40 min post arrest, respectively. Enrichment peaks indicate the midpoints of nucleosome positions, and determined nucleosome locations are represented below by circles with two diagonal lines, in agreement with previous work ( 12 , 57 ). Swi5 binding sites are indicated by blue rectangular boxes and determined NDRs are indicated by arrows.…”

FACT mediates cohesin function on chromatin

“…4). Recently, an involvement of FACT in chromatin architecture independent of transcription has been proposed 36 , our data suggests that this function might be related to cohesin's role in genome architecture. We speculate that similar to its roles in transcription and replication, FACT function as a histone chaperone is likely to occur through destabilization of core nucleosomal particles, to allow movement of cohesins on chromatin.…”

The Chaperone FACT and Histone H2B Ubiquitination Maintain S. pombe Genome Architecture through Genic and Subtelomeric Functions

“…Indeed, it was suggested that the ongoing cryptic transcription in the spt16 mutant leads to histone loss in S. cerevisiae (Feng et al, 2016). Our results cannot exclude the possibility that the +1 nucleosome has an antisense barrier function (McCullough et al, 2019) and that FACT is important for the establishment of this barrier.…”