Singh, T. R. et al. MHF1-MHF2, a histone-fold-containing protein complex, participates in the Fanconi anemia pathway via FANCM. Mol. Cell 37, 879-886

Division of Experimental Hematology and Cancer Biology, Cincinnati Children's Research Foundation and University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA.
Molecular cell (Impact Factor: 14.02). 03/2010; 37(6):879-86. DOI: 10.1016/j.molcel.2010.01.036
Source: PubMed


FANCM is a Fanconi anemia nuclear core complex protein required for the functional integrity of the FANC-BRCA pathway of DNA damage response and repair. Here we report the isolation and characterization of two histone-fold-containing FANCM-associated proteins, MHF1 and MHF2. We show that suppression of MHF1 expression results in (1) destabilization of FANCM and MHF2, (2) impairment of DNA damage-induced monoubiquitination and foci formation of FANCD2, (3) defective chromatin localization of FA nuclear core complex proteins, (4) elevated MMC-induced chromosome aberrations, and (5) sensitivity to MMC and camptothecin. We also provide biochemical evidence that MHF1 and MHF2 assemble into a heterodimer that binds DNA and enhances the DNA branch migration activity of FANCM. These findings reveal critical roles of the MHF1-MHF2 dimer in DNA damage repair and genome maintenance through FANCM.

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    • "We identified CenpI, CenpL/M/N, and the DNA-proximal CenpS/X proteins. We note that since the CenpT/W proteins, which are obligatory for the CenpS/X kinetochore function, are absent in all insects, it is likely that the CenpS/X complex serves roles in DNA damage (Singh et al., 2010) rather than at the kinetochore. Nonetheless, several inner kinetochore components continue to be present even in the CenH3-deficient species (Figure 2A). "
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    ABSTRACT: Faithful chromosome segregation in all eukaryotes relies on centromeres, the chromosomal sites that recruit kinetochore proteins and mediate spindle attachment during cell division. The centromeric histone H3 variant, CenH3, is the defining chromatin component of centromeres in most eukaryotes, including animals, fungi, plants, and protists. In this study, using detailed genomic and transcriptome analyses, we show that CenH3 was lost independently in at least four lineages of insects. Each of these lineages represents an independent transition from monocentricity (centromeric determinants localized to a single chromosomal region) to holocentricity (centromeric determinants extended over the entire chromosomal length) as ancient as 300 million years ago. Holocentric insects therefore contain a CenH3-independent centromere, different from almost all the other eukaryotes. We propose that ancient transitions to holocentricity in insects obviated the need to maintain CenH3, which is otherwise essential in most eukaryotes, including other holocentrics.
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    • "This suggests that CENP-T-W and CENP-S-X can function independently. Indeed, CENP-S-X binds FANCM proteins at DNA damage sites (Singh et al., 2010; Yan et al., 2010). Further studies are needed to clarify how CENP-T-W, CENP-S-X, and CENP-T-W-S-X bind to DNA and how the tetramer contributes to formation of centromeric chromatin. "
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    ABSTRACT: Since discovery of the centromere-specific histone H3 variant CENP-A, centromeres have come to be defined as chromatin structures that establish the assembly site for the complex kinetochore machinery. In most organisms, centromere activity is defined epigenetically, rather than by specific DNA sequences. In this review, we describe selected classic work and recent progress in studies of centromeric chromatin with a focus on vertebrates. We consider possible roles for repetitive DNA sequences found at most centromeres, chromatin factors and modifications that assemble and activate CENP-A chromatin for kinetochore assembly, plus the use of artificial chromosomes and kinetochores to study centromere function.
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    • "CENP–S and CENP–X also form a tetramer in the absence of CENP–T–W. Whereas the CENP–T–W–S–X complex localizes to kinetochores, the CENP–S–X complex associates with FANCM and is targeted to DNA damage sites in the absence of CENP–T–W (25,26). Despite the distinct function of these complexes, the structure of the CENP–T–W–S–X complex is similar to that of the CENP–S–X complex (12). "
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    ABSTRACT: The centromere is a specific genomic region upon which the kinetochore is formed to attach to spindle microtubules for faithful chromosome segregation. To distinguish this chromosomal region from other genomic loci, the centromere contains a specific chromatin structure including specialized nucleosomes containing the histone H3 variant CENP-A. In addition to CENP-A nucleosomes, we have found that centromeres contain a nucleosome-like structure comprised of the histone-fold CENP-T-W-S-X complex. However, it is unclear how the CENP-T-W-S-X complex associates with centromere chromatin. Here, we demonstrate that the CENP-T-W-S-X complex binds preferentially to ∼100 bp of linker DNA rather than nucleosome-bound DNA. In addition, we find that the CENP-T-W-S-X complex primarily binds to DNA as a (CENP-T-W-S-X)2 structure. Interestingly, in contrast to canonical nucleosomes that negatively supercoil DNA, the CENP-T-W-S-X complex induces positive DNA supercoils. We found that the DNA-binding regions in CENP-T or CENP-W, but not CENP-S or CENP-X, are required for this positive supercoiling activity and the kinetochore targeting of the CENP-T-W-S-X complex. In summary, our work reveals the structural features and properties of the CENP-T-W-S-X complex for its localization to centromeres.
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