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Protein ubiquitination at sites of DNA double-strand breaks (DSBs) by RNF168 recruits BRCA1 and 53BP1.sup.1,2, which are mediators of the homologous recombination and non-homologous end joining DSB repair pathways, respectively.sup.3. Non-homologous end joining relies on 53BP1 binding directly to ubiquitinated lysine 15 on H2A-type histones (H2AK15ub).sup.4,5 (which is an RNF168-dependent modification.sup.6), but how RNF168 promotes BRCA1 recruitment and function remains unclear. Here we identify a tandem BRCT-domain-associated ubiquitin-dependent recruitment motif (BUDR) in BRCA1-associated RING domain protein 1 (BARD1) (the obligate partner protein of BRCA1) that, by engaging H2AK15ub, recruits BRCA1 to DSBs. Disruption of the BUDR of BARD1 compromises homologous recombination and renders cells hypersensitive to PARP inhibition and cisplatin. We further show that BARD1 binds nucleosomes through multivalent interactions: coordinated binding of H2AK15ub and unmethylated H4 lysine 20 by its adjacent BUDR and ankyrin repeat domains, respectively, provides high-affinity recognition of DNA lesions in replicated chromatin and promotes the homologous recombination activities of the BRCA1-BARD1 complex. Finally, our genetic epistasis experiments confirm that the need for BARD1 chromatin-binding activities can be entirely relieved upon deletion of RNF168 or 53BP1. Thus, our results demonstrate that by sensing DNA-damage-dependent and post-replication histone post-translation modification states, BRCA1-BARD1 complexes coordinate the antagonization of the 53BP1 pathway with promotion of homologous recombination, establishing a simple paradigm for the governance of the choice of DSB repair pathway. A tandem BRCT-domain-associated ubiquitin-dependent recruitment motif in BARD1 recruits BRCA1 to DNA double-strand breaks (DSBs) to promote homologous recombination and antagonize the 53BP1 DSB repair pathway that mediates non-homologous end joining., Author(s): Jordan R. Becker [sup.1] [sup.2] , Gillian Clifford [sup.3] , Clara Bonnet [sup.1] [sup.2] , Anja Groth [sup.4] [sup.5] , Marcus D. Wilson [sup.3] , J. Ross Chapman [sup.1] [...]

We have a limited understanding of how cells mark and identify newly replicated genomic loci that have a sister chromatid; here, unmethylated K20 in the tail of new histone H4 is shown to serve as a signature of post-replicative chromatin, which is specifically recognized by the homologous recombination complex TONSL-MMS22L. A marker for post-replicative chromatin We have a limited understanding of how cells mark and identify newly replicated genomic loci that have a sister chromatid. Here, Anja Groth and colleagues show that histone H4 tails unmethylated at lysine 20 (H4K20me0) serve as a signature of post-replicative chromatin and are specific to new histones incorporated during DNA replication. H4K20me0 is specifically recognized by a 'reader' domain of the TONSL-MMS22L homologous recombination complex, enabling differentiation of pre- and post-replicative chromatin, and allowing TONSL to function as a histone chaperone or guide repair of damaged replication forks. After DNA replication, chromosomal processes including DNA repair and transcription take place in the context of sister chromatids. While cell cycle regulation can guide these processes globally, mechanisms to distinguish pre- and post-replicative states locally remain unknown. Here we reveal that new histones incorporated during DNA replication provide a signature of post-replicative chromatin, read by the human TONSL-MMS22L.sup.1,2,3,4 homologous recombination complex. We identify the TONSL ankyrin repeat domain (ARD) as a reader of histone H4 tails unmethylated at K20 (H4K20me0), which are specific to new histones incorporated during DNA replication and mark post-replicative chromatin until the G2/M phase of the cell cycle. Accordingly, TONSL-MMS22L binds new histones H3-H4 both before and after incorporation into nucleosomes, remaining on replicated chromatin until late G2/M. H4K20me0 recognition is required for TONSL-MMS22L binding to chromatin and accumulation at challenged replication forks and DNA lesions. Consequently, TONSL ARD mutants are toxic, compromising genome stability, cell viability and resistance to replication stress. Together, these data reveal a histone-reader-based mechanism for recognizing the post-replicative state, offering a new angle to understand DNA repair with the potential for targeted cancer therapy., Author(s): Giulia Saredi [sup.1] , Hongda Huang [sup.2] , Colin M. Hammond [sup.1] , Constance Alabert [sup.1] , Simon Bekker-Jensen [sup.3] , Ignasi Forne [sup.4] , Nazaret Reverón-Gómez [sup.1] , [...]

Chromatin serves structural and functional roles crucial for genome stability and correct gene expression. This organization must be reproduced on daughter strands during replication to maintain proper overlay of epigenetic fabric onto genetic sequence. Nucleosomes constitute the structural framework of chromatin and carry information to specify higher-order organization and gene expression. When replication forks traverse the chromosomes, nucleosomes are transiently disrupted, allowing the replication machinery to gain access to DNA. Histone recycling, together with new deposition, ensures reassembly on nascent DNA strands. The aim of this review is to discuss how histones--new and old are handled at the replication fork, highlighting new mechanistic insights and revisiting old paradigms. Key words: histone chaperones, chromatin, DNA replication, Asf1, MCM, FACT. La chromatine joue plusieurs roles structurels et fonctionnels cruciaux pour la stabilite du genome et l'expression genique adequate. Cette organisation doit etre reproduite chez les molecules filles des brins d' ADN lors de la replication afin de maintenir un schema correct de la trame epigenetique dans la sequence genetique. Les nucleosomes constituent le canevas structurel de la chromatine et contiennent l'information necessaire a la specification d'un ordre d'organisation plus eleve et a l'expression genique. Lorsque la fourche de replication traverse les chromosomes, les nucleosomes sont desorganises de facon transitoire, permettant a la machinerie de la replication d'avoir acces a l'ADN. Le recyclage et le nouveau depot des histones permettent leur reassemblage sur les brins d'ADN nouvellement formes. Le but de cet article de revue est de discuter de la facon dont les histones (nouvelles et anciennes) sont prises en charge a la fourche de replication, mettant en evidence de nouveaux apercus des mecanismes impliques et revisitant les paradigmes anciens. Mots-cles : histones, nucleosomes, chaperons, chromatine, epigenetique, replication d'ADN, Asf1, MCM, FACT. [Traduit par la Redaction], Introduction Chromatin-based inheritance is instrumental during development, when genome information must be used selectively to shape a highly complex organism, and stochastic changes in chromatin may be a driving force [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2007.01.030 Byline: Anja Groth (1), Walter Rocha (2), Alain Verreault (2), Genevieve Almouzni (1) Abstract: Inheritance and maintenance of the DNA sequence and its organization into chromatin are central for eukaryotic life. To orchestrate DNA-replication and -repair processes in the context of chromatin is a challenge, both in terms of accessibility and maintenance of chromatin organization. To meet the challenge of maintenance, cells have evolved efficient nucleosome-assembly pathways and chromatin-maturation mechanisms that reproduce chromatin organization in the wake of DNA replication and repair. The aim of this Review is to describe how these pathways operate and to highlight how the epigenetic landscape may be stably maintained even in the face of dramatic changes in chromatin structure. Author Affiliation: (1) Laboratory of Nuclear Dynamics and Genome Plasticity, UMR 218 CNRS/Institut Curie, 26 rue d'Ulm, 75248 Paris, Cedex 5, France (2) Institute for Research in Immunology and Cancer, University of Montreal, PO Box 6128, Succursale Centre-Ville, Montreal, QC H3C 3J7, Canada