An Additional Replication Origin Causes Cell Cycle Specific DNA Replication Fork Speed.
DNA RFS (replication fork speed) was determined in E. coli strains - with either one or with two origins of  replication - using marker frequency analysis of deep sequencing data. Our analysis revealed  that RFS is reduced by approximately one third when four replication forks are active and increases  by about one fourth when only one fork is active, resulting in a twofold variation in RFS during the replication cycle. Moreover, delaying replication initiation or increasing the available dNTP pool normalized these variations, indicating that nucleotide supply is the primary constraint on replication  speed. These findings demonstrate that RFS is not inherently constant within a replication cycle and  provide a basis for further studies into the factors that regulate replication kinetics.