Termination Structures in the Escherichia coli Chromosome Replication Fork Trap |
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Authors: | Iain G Duggin Stephen D Bell |
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Institution: | Medical Research Council Cancer Cell Unit, Hutchison-Medical Research Council Research Centre, Hills Road, Cambridge CB2 0XZ, UK Sir William Dunn School of Pathology, University of Oxford, South Parks Road, Oxford OX1 3RE, UK |
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Abstract: | The Escherichia coli chromosome contains two opposed sets of unidirectional DNA replication pause (Ter) sites that, according to the replication fork trap theory, control the termination of chromosome replication by restricting replication fork fusion to the terminus region. In contrast, a recent hypothesis suggested that termination occurs at the dif locus instead. Using two-dimensional agarose gel electrophoresis, we examined DNA replication intermediates at the Ter sites and at dif in wild-type cells. Two definitive signatures of site-specific termination—specific replication fork arrest and converging replication forks—were clearly detected at Ter sites, but not at dif. We also detected a significant pause during the latter stages of replication fork convergence at Ter sites. Quantification of fork pausing at the Ter sites in both their native chromosomal context and the plasmid context further supported the fork trap model. |
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Keywords: | oriC chromosomal replication origin 2D two-dimensional pTer pseudo-Ter |
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