Abstract
On both procaryotic and eucaryotic genomes, there are specific sites at which progress of DNA replication is impeded. Analysis of the fork-blocking systems in E.coli and yeast has revealed their molecular mechanisms. During the course of experiments in E.coli, we found out that a DNA region close to the fork-blocking site is recombinationally activated. Analysis of this phenomenon revealed that organisms have a system, which has ability to destroy the arrested fork and to reconstruct a new replication fork to overcome the obstacle. This rescue system of the fork is really a homologous recombination system in itself. Surprisingly, in yeast the fork-blocking system plays a central role in increase and decrease in copy number of the ribosomal RNA gene through efficient recombination. Suggesting that fork blockage may contribute to various structural changes of genomes more than expected.
