Book of Abstracts: Albany 2011
June 14-18 2011
©Adenine Press (2010)
Essential role of the Rep, UvrD and DinG Helicases and of the RecBC Recombination Complex upon Replication – Transcription Collisions in the E. coli Chromosome
We are interested in the consequences of replication fork arrest in bacteria. We characterized several different reactions occurring at blocked forks prior to replication restart, which depend on the cause of arrest (reviewed in 1). Recently, we used Escherichia coli strains carrying inverted ribosomal operons (rrn) in order to analyze replication arrest caused by replication-transcription collisions. We identified three helicases required for replication upon head-on collision with transcription complexes: the Rep, UvrD and DinG helicases (2). Replication arrest sites could be directly visualized in ribosomal operons facing replication (provided that Rep or DinG was inactivated), and the inactivation of any combination of two of these three accessory replicative helicases was highly detrimental for viability. All three helicases are involved in RNA Pol removal, and DinG has an additional function of R-loop removal. In E. coli, rep uvrD and rep uvrD dinG recF mutants grow poorly particularly on rich medium (multiple replication forks conditions). We isolated mutations that suppress these growth defects; all map in RNA polymerase genes and presumably facilitate RNA Pol dislodging from DNA, which supports the idea that the Rep, UvrD and DinG helicases also facilitate replication across transcribed regions in wild-type E. coli cells (3). In addition, increasing replication-transcription collisions by inverting an rrn operon creates a requirement for the recombination complex RecBC, specific for the degradation and the recombinational repair of DNA double-strand ends. However, the key homologous recombination protein RecA is not required, suggesting a specific role for RecBC. The role of recombination proteins upon replication-transcription collisions will be discussed.
Anne Langlois de Septenville
CNRS, Centre de Génétique Moléculaire, UPR3404, Gif-sur-Yvette, F-91198, France