Initiation of the DNA replication cycle in Escherichia coli linkage of origin daughter DNA to parental DNA?

Abstract

Many models for the mechanism of initiation of DNA replication in bacteria include the idea that DNA synthesis is initiated at the 3t́-OH end of a parental DNA strand. We have tried to determine whether the initiation of DNA replication in Escherichia coli involves covalent joining of origin daughter DNA to pre-existing parental DNA. The technique used to visualize such a linkage was a density shift from 5-bromouracil to thymine at the time of initiation of a cycle of DNA replication. When such a density shift is made during DNA chain elongation, intermediate density DNA fragments due to transition points are observed, but when the density shift is made at the time of initiation of new rounds of DNA replication, intermediate density DNA fragments due to linkage of origin daughter DNA to parental DNA are not found. These results indicate that if DNA replication in E. coli is initiated by linkage to parental DNA, such linkage persists for less than one to two minutes.