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Nat Cell Biol January 1, 2016; 18 (6): 684-91.

Centromeric DNA replication reconstitution reveals DNA loops and ATR checkpoint suppression.

Aze A , Sannino V , Soffientini P , Bachi A , Costanzo V .

Half of the human genome is made up of repetitive DNA. However, mechanisms underlying replication of chromosome regions containing repetitive DNA are poorly understood. We reconstituted replication of defined human chromosome segments using bacterial artificial chromosomes in Xenopus laevis egg extract. Using this approach we characterized the chromatin assembly and replication dynamics of centromeric alpha-satellite DNA. Proteomic analysis of centromeric chromatin revealed replication-dependent enrichment of a network of DNA repair factors including the MSH2-6 complex, which was required for efficient centromeric DNA replication. However, contrary to expectations, the ATR-dependent checkpoint monitoring DNA replication fork arrest could not be activated on highly repetitive DNA due to the inability of the single-stranded DNA binding protein RPA to accumulate on chromatin. Electron microscopy of centromeric DNA and supercoil mapping revealed the presence of topoisomerase I-dependent DNA loops embedded in a protein matrix enriched for SMC2-4 proteins. This arrangement suppressed ATR signalling by preventing RPA hyper-loading, facilitating replication of centromeric DNA. These findings have important implications for our understanding of repetitive DNA metabolism and centromere organization under normal and stressful conditions.

PubMed ID: 27111843
PMC ID: PMC4939857
Article link: Nat Cell Biol
Grant support: [+]

Species referenced: Xenopus
Genes referenced: atr gem gmnn il17f msh2 msh3 msh4 msh5 msh6 rpa1 smc2

Article Images: [+] show captions
References [+] :
Amiard, A topological mechanism for TRF2-enhanced strand invasion. 2007, Pubmed