WHEN REPLICATION FORKS STOP

DNA synthesis is an accurate and very processive phenomenon, yet chrom osome replication does not proceed at a constant rate and progression of the replication fork can be impeded. Several structural and functio nal features of the template can modulate the rate of progress of the replication fork. These include DNA secondary structures, DNA damage a nd occupied protein-binding sites. In addition, prokaryotes contain si tes where replication is specifically arrested. DNA regions at which t he replication machinery is blocked or transiently slowed could be par ticularly susceptible to genome rearrangements. Illegitimate recombina tion, a ubiquitous phenomenon which may have dramatic consequences, oc curs by a variety of mechanisms. The observation that some rearrangeme nts might be facilitated by a pause in replication could provide a clu e in elucidating these processes. In support of this, some homologous and illegitimate recombination events have already been correlated wit h replication pauses or arrest sites.