Nucleic Acids Research Advance Access originally published online on August 23, 2007
Nucleic Acids Research 2007 35(17):5763-5774; doi:10.1093/nar/gkm586
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Nucleic Acids Research, 2007, Vol. 35, No. 17 5763-5774
© 2007 The Author(s)
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Molecular Biology |
Low rate of replication fork progression lengthens the replication timing of a locus containing an early firing origin
CNRS-FRE 2937, Institut André Lwoff, BP8, 94800 Villejuif, France
*To whom correspondence should be addressed. Tel: 33 1 49 58 33 73; Fax: 33 1 49 58 33 81; Email: benard{at}vjf.cnrs.fr
Received May 18, 2007. Revised July 11, 2007. Accepted July 17, 2007.
Invariance of temporal order of genome replication in eukaryotic cells and its correlation with gene activity has been well-documented. However, recent data suggest a relax control of replication timing. To evaluate replication schedule accuracy, we detailed the replicational organization of the developmentally regulated php locus that we previously found to be lately replicated, even though php gene is highly transcribed in naturally synchronous plasmodia of Physarum. Unexpectedly, bi-dimensional agarose gel electrophoreses of DNA samples prepared at specific time points of S phase showed that replication of the locus actually begins at the onset of S phase but it proceeds through the first half of S phase, so that complete replication of php-containing DNA fragments occurs in late S phase. Origin mapping located replication initiation upstream php coding region. This proximity and rapid fork progression through the coding region result in an early replication of php gene. We demonstrated that afterwards an unusually low fork rate and unidirectional fork pausing prolong complete replication of php locus, and we excluded random replication timing. Importantly, we evidenced that the origin linked to php gene in plasmodium is not fired in amoebae when php expression dramatically reduced, further illustrating replication-transcription coupling in Physarum.