High-Resolution Mapping of Points of Site-Specific Replication Stalling

Genetic instability due to stalled replication forks is thought to underlie a number of human diseases, such as premature ageing and cancer susceptibility syndromes. In addition, site-specific stalling occurs at some genetic loci. A detailed understanding of the topology of the stalled replication fork gives a valuable insight into the causes and mechanisms of replication stalling. The method described here allows mapping of the position of the 3′-end of the nascent leading or lagging strand at the replication fork, stalled at a site-specific barrier. The replicating DNA is purified, digested with restriction enzymes, and enriched by BND-cellulose chromatography. The DNA is separated on a sequencing gel, transferred to a membrane, and hybridised to a strand-specific probe. The data obtained using this method allow determining the position of the 3′-end of the nascent strand at a stalled fork with a one-nucleotide resolution.