Article
- The EMBO Journal (2009) 28, 1666 - 1678
- doi:10.1038/emboj.2009.125
Published online: 14 May 2009
Subject Categories:
Plasmid replication initiator RepB forms a hexamer reminiscent of ring helicases and has mobile nuclease domains
D Roeland Boer1,2, José A Ruíz-Masó3, José R López-Blanco3, Alexander G Blanco1,2, Mireia Vives-Llàcer1,2, Pablo Chacón3, Isabel Usón2,4, F Xavier Gomis-Rüth2, Manuel Espinosa3, Oscar Llorca3, Gloria del Solar3 and Miquel Coll1,2
- Institute for Research in Biomedicine, Barcelona Science Park, Barcelona, Spain
- Institut de Biologia Molecular de Barcelona, CSIC, Barcelona Science Park, Barcelona, Spain
- Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu, Madrid, Spain
- Institució Catalana de Recerca i Estudis Avançats (ICREA), Barcelona, Spain
Correspondence to:
Gloria del Solar, Centro de Investigaciones Biológicas, CSIC, Ramiro de Maeztu, 9, 28040 Madrid, Spain. Tel.: +34 91 8373112; Fax: +34 91 5360432; E-mail: gdelsolar@cib.csic.es
Miquel Coll, Institute for Research in Biomedicine, Barcelona Science Park, Baldiri Reixac 10, Barcelona 08028, Spain. Tel.: +34 93 4034951; Fax: +34 93 4034979; E-mail: miquel.coll@irbbarcelona.org
Received 6 November 2008; Accepted 7 April 2009
Abstract
RepB initiates plasmid rolling-circle replication by binding to a triple 11-bp direct repeat (bind locus) and cleaving the DNA at a specific distant site located in a hairpin loop within the nic locus of the origin. The structure of native full-length RepB reveals a hexameric ring molecule, where each protomer has two domains. The origin-binding and catalytic domains show a three-layer 
–
– sandwich fold. The active site is positioned at one of the faces of the -sheet and coordinates a Mn2+ ion at short distance from the essential nucleophilic Y99. The oligomerization domains (ODs), each consisting of four -helices, together define a compact ring with a central channel, a feature found in ring helicases. The toroidal arrangement of RepB suggests that, similar to ring helicases, it encircles one of the DNA strands during replication to confer processivity to the replisome complex. The catalytic domains appear to be highly mobile with respect to ODs. This mobility may account for the adaptation of the protein to two distinct DNA recognition sites.
Keywords:
- DNA-binding protein,
- nuclease,
- plasmid replication,
- replication initiator,
- X-ray crystal structure
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