Barcelona BioMed Seminars

Dual Roles of Poly(dA:dT) Tracts in Replication Initiation and Fork Collapse

4 Oct 2018

Speaker:  Andre Nussenzweig, Ph.D. NIH Distinguished Investigator. Center for Cancer Research National Cancer Institute. Bethesda, Maryland (US)

Organizers: IRB Barcelona
Date: Thursday 04 October 2018, 12.00h
Place: Aula Fèlix Serratosa, Parc Científic de Barcelona, Spain

Host: Dr. Travis Stracker

Abstract

Replication origins, fragile sites, and rDNA have been implicated as sources of chromosomal instability. However, the defining genomic features of replication origins and fragile sites are among the least understood elements of eukaryote genomes. Here, we map sites of replication initiation and breakage in primary cells at high resolution. We find that replication initiates between transcribed genes within nucleosome-depleted structures established by long asymmetrical poly(dA:dT) tracts flanking the initiation site. Paradoxically, long (>20 bp) (dA:dT) tracts are also preferential sites of polar replication fork stalling and collapse within early-replicating fragile sites (ERFSs) and late-replicating common fragile sites (CFSs) and at the rDNA replication fork barrier. Poly(dA:dT) sequences are fragile because long single-strand poly(dA) stretches at the replication fork are unprotected by the replication protein A (RPA). We propose that the evolutionary expansion of poly(dA:dT) tracts in eukaryotic genomes promotes replication initiation, but at the cost of chromosome fragility.

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