The histone chaperone FACT modulates nucleosome structure by tethering its components

AbstractHuman FACT (hFACT) is a conserved histone chaperone that was originally described as a transcription elongation factor with potential nucleosome assembly functions. Here we show that FACT facilitates tetrasome assembly and H2A-H2B deposition to form hexasomes and nucleosomes. In the process, FACT tethers components of the nucleosome through interactions with H2A-H2B, resulting in a defined intermediate complex comprised of FACT, a histone hexamer and DNA. Free DNA extending from the tetrasome then competes FACT off H2A-H2B, thereby promoting hexasome and nucleosome formation. Our studies provide mechanistic insight into how FACT may stabilize partial nucleosome structures during transcription or nucleosome assembly, seemingly facilitating nucleosome disassembly and nucleosome assembly.

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The histone chaperone FACT modulates nucleosome structure by tethering its components

Life Science Alliance ◽

10.26508/lsa.201800107 ◽

2018 ◽

Vol 1 (4) ◽

pp. e201800107 ◽

Cited By ~ 28

Author(s):

Tao Wang ◽

Yang Liu ◽

Garrett Edwards ◽

Daniel Krzizike ◽

Hataichanok Scherman ◽

...

Keyword(s):

Elongation Factor ◽

Histone Chaperone ◽

Nucleosome Assembly ◽

Transcription Elongation Factor ◽

Nucleosome Structure ◽

Mechanistic Insight ◽

Nucleosome Formation ◽

Nucleosome Disassembly ◽

Assembly Activity ◽

Insight Into

Human FAcilitates Chromatin Transcription (hFACT) is a conserved histone chaperone that was originally described as a transcription elongation factor with potential nucleosome assembly functions. Here, we show that FACT has moderate tetrasome assembly activity but facilitates H2A–H2B deposition to form hexasomes and nucleosomes. In the process, FACT tethers components of the nucleosome through interactions with H2A–H2B, resulting in a defined intermediate complex comprising FACT, a histone hexamer, and DNA. Free DNA extending from the tetrasome then competes FACT off H2A–H2B, thereby promoting hexasome and nucleosome formation. Our studies provide mechanistic insight into how FACT may stabilize partial nucleosome structures during transcription or nucleosome assembly, seemingly facilitating both nucleosome disassembly and nucleosome assembly.

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Ribosome collisions alter frameshifting at translational reprogramming motifs in bacterial mRNAs

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1910613116 ◽

2019 ◽

Vol 116 (43) ◽

pp. 21769-21779 ◽

Cited By ~ 10

Author(s):

Angela M. Smith ◽

Michael S. Costello ◽

Andrew H. Kettring ◽

Robert J. Wingo ◽

Sean D. Moore

Keyword(s):

Ribosomal Protein ◽

Strong Dependence ◽

Elongation Factor ◽

Messenger Rnas ◽

Reading Frame ◽

Translational Frameshifting ◽

Naturally Occurring ◽

Mechanistic Insight ◽

Mrna Pool ◽

Insight Into

Translational frameshifting involves the repositioning of ribosomes on their messages into decoding frames that differ from those dictated during initiation. Some messenger RNAs (mRNAs) contain motifs that promote deliberate frameshifting to regulate production of the encoded proteins. The mechanisms of frameshifting have been investigated in many systems, and the resulting models generally involve single ribosomes responding to stimulator sequences in their engaged mRNAs. We discovered that the abundance of ribosomes on messages containing the IS3, dnaX, and prfB frameshift motifs significantly influences the levels of frameshifting. We show that this phenomenon results from ribosome collisions that occur during translational stalling, which can alter frameshifting in both the stalled and trailing ribosomes. Bacteria missing ribosomal protein bL9 are known to exhibit a reduction in reading frame maintenance and to have a strong dependence on elongation factor P (EFP). We discovered that ribosomes lacking bL9 become compacted closer together during collisions and that the E-sites of the stalled ribosomes appear to become blocked, which suggests subsequent transpeptidation in transiently stalled ribosomes may become compromised in the absence of bL9. In addition, we determined that bL9 can suppress frameshifting of its host ribosome, likely by regulating E-site dynamics. These findings provide mechanistic insight into the behavior of colliding ribosomes during translation and suggest naturally occurring frameshift elements may be regulated by the abundance of ribosomes relative to an mRNA pool.

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The role of FACT in managing chromatin: disruption, assembly, or repair?

Nucleic Acids Research ◽

10.1093/nar/gkaa912 ◽

2020 ◽

Vol 48 (21) ◽

pp. 11929-11941

Author(s):

Tim Formosa ◽

Fred Winston

Keyword(s):

Dna Repair ◽

Dna Replication ◽

Normal State ◽

Elongation Factor ◽

Histone Chaperone ◽

The Core ◽

Transcription Elongation Factor ◽

Differentiated Cells ◽

Chromatin Integrity

Abstract FACT (FAcilitates Chromatin Transcription) has long been considered to be a transcription elongation factor whose ability to destabilize nucleosomes promotes RNAPII progression on chromatin templates. However, this is just one function of this histone chaperone, as FACT also functions in DNA replication. While broadly conserved among eukaryotes and essential for viability in many organisms, dependence on FACT varies widely, with some differentiated cells proliferating normally in its absence. It is therefore unclear what the core functions of FACT are, whether they differ in different circumstances, and what makes FACT essential in some situations but not others. Here, we review recent advances and propose a unifying model for FACT activity. By analogy to DNA repair, we propose that the ability of FACT to both destabilize and assemble nucleosomes allows it to monitor and restore nucleosome integrity as part of a system of chromatin repair, in which disruptions in the packaging of DNA are sensed and returned to their normal state. The requirement for FACT then depends on the level of chromatin disruption occurring in the cell, and the cell's ability to tolerate packaging defects. The role of FACT in transcription would then be just one facet of a broader system for maintaining chromatin integrity.

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