The replisome uses mRNA as a primer after colliding with RNA polymerase

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Replication forks are impeded by DNA damage and protein–nucleic acid complexes such as transcribing RNA polymerase. For example, head-on collision of the replisome with RNA polymerase results in replication fork arrest. However, co-directional collision of the replisome with RNA polymerase has little or no effect on fork progression. Here we examine co-directional collisions between a replisome and RNA polymerase in vitro. We show that the Escherichia coli replisome uses the RNA transcript as a primer to continue leading-strand synthesis after the collision with RNA polymerase that is displaced from the DNA. This action results in a discontinuity in the leading strand, yet the replisome remains intact and bound to DNA during the entire process. These findings underscore the notable plasticity by which the replisome operates to circumvent obstacles in its path and may explain why the leading strand is synthesized discontinuously in vivo.

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Figure 1: Leading-strand synthesis is interrupted by a co-directional RNA polymerase.
Figure 2: The replisome extends the transcript of a co-directional RNA polymerase.
Figure 3: The replisome remains intact and displaces a co-directional RNA polymerase from the DNA.
Figure 4: Replisome bypass of a co-directional E. coli RNAP elongation complex.
Figure 5: Model of replisome bypass of a co-directional RNA polymerase.


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We are grateful to W. T. McAllister and R. Castagna for providing T7 RNAP, and to S. Darst and L. Westblade for providing E. coli RNAP proteins and plasmids. This work was supported by a grant from the National Institutes of Health (M.O.D.) and by a Marie-Josee and Henry Kravis Fellowship at the Rockefeller University (R.T.P.).

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Correspondence to Mike O’Donnell.

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Pomerantz, R., O’Donnell, M. The replisome uses mRNA as a primer after colliding with RNA polymerase. Nature 456, 762–766 (2008) doi:10.1038/nature07527

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