No abstract

CIA (CCG1-interacting factor A)/ASF1, which is the most conserved histone chaperone among the eukaryotes, was genetically identified as a factor for an anti-silencing function (Asf1) by yeast genetic screening. Shortly after that, the CIA-histone-H3-H4 complex was isolated from Drosophila as a histone chaperone CAF-1 stimulator. Human CIA-I/II (ASF1a/b) was identified as a histone chaperone that interacts with the bromodomain-an acetylated-histone-recognizing domain-of CCG1, in the general transcription initiation factor TFIID. Intensive studies have revealed that CIA/ASF1 mediates nucleosome assembly by forming a complex with another histone chaperone in human cells and yeast, and is involved in DNA replication, transcription, DNA repair and silencing/anti-silencing in yeast. CIA/ASF1 was shown as a major storage chaperone for soluble histones in proliferating human cells. Despite all these biochemical and biological functional analyses, the structure-function relationship of the nucleosome assembly/disassembly activity of CIA/ASF1 has remained elusive. Here we report the crystal structure, at 2.7 A resolution, of CIA-I in complex with histones H3 and H4. The structure shows the histone H3-H4 dimer's mutually exclusive interactions with another histone H3-H4 dimer and CIA-I. The carboxy-terminal beta-strand of histone H4 changes its partner from the beta-strand in histone H2A to that of CIA-I through large conformational change. In vitro functional analysis demonstrated that CIA-I has a histone H3-H4 tetramer-disrupting activity. Mutants with weak histone H3-H4 dimer binding activity showed critical functional effects on cellular processes related to transcription. The histone H3-H4 tetramer-disrupting activity of CIA/ASF1 and the crystal structure of the CIA/ASF1-histone-H3-H4 dimer complex should give insights into mechanisms of both nucleosome assembly/disassembly and nucleosome semi-conservative replication.

Some three decades have passed since the discovery of nucleosomes in 1974 and the first isolation of a histone chaperone in 1978. While various types of histone chaperones have been isolated and functionally analyzed, the elementary processes of nucleosome assembly and disassembly have been less well characterized. Recently, the tertiary structure of a hetero-trimeric complex composed of the histone chaperone CIA/ASF1 and the histone H3-H4 dimer was determined, and this complex was proposed to be an intermediate in nucleosome assembly and disassembly reactions. In addition, CIA alone was biochemically shown to dissociate the histone (H3-H4)2 tetramer into two histone H3-H4 dimers. This activity suggested that CIA regulates the semi-conservative replication of nucleosomes. Here, we provide an overview of prominent histone chaperones with the goal of elucidating the mechanisms that preserve and modify epigenetic information. We also discuss the reactions involved in nucleosome assembly and disassembly.

for the first time. These observations lead to a mechanism of RapAmediated RNAP recycling, including the RapA-facilitated release of sequestered RNAP from DNA template and the σ70-dependent removal of RapA from the RapA•CORE complex for transcription reinitiation. The derived mechanism of RapA provides a framework for further structural and biochemical investigations on, for example, how and where RNAP becomes sequestered in the PTC, the exact composition of the PTC, the DNA translocase activity of RapA and its precise mechanism, and additional factors that may contribute to the destabilization of the PTC.

sity-Objectives: The aim of this study was to investigate workplace violence by patients or their relatives towards health-care workers in Congolese hospitals. Methods: Through the autumn of 2012, a crosssectional survey on workplace violence was conducted in a sample of 2,210 registered health-care workers (989 males and 1,221 females, aged 33 ± 8 years) from 436 hospitals located in the province of Katanga, Democratic Republic of the Congo. Verbal aggression, harassment and physical violence perpetrated by patients or their relatives within the previous year along with factors contributing to violence, were recorded, and the response rate was 99%. Results: About 80.1% of the health-care workers had experienced one or more types of workplace violence. Overall, the severity of workplace violence varied from verbal aggression (57.4%) and harassment (15.2%) to physical violence (7.5%). Patients were the major perpetrators of verbal aggression and harassment, whereas patients' relatives were mainly involved in physical violence. The frequency of workplace violence was similar across hospitals. Male health-care workers were more likely to be victims of physical violence, whereas female health-care workers were the prime target for harassment. Only 34.3% of the violent episodes were reported to a supervisor.