Nucleic Acids Research Advance Access originally published online on September 4, 2009
Nucleic Acids Research 2009 37(19):6540-6549; doi:10.1093/nar/gkp685
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Nucleic Acids Research, 2009, Vol. 37, No. 19 6540-6549
© The Author(s) 2009. Published by Oxford University Press.
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
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SrmB, a DEAD-box helicase involved in Escherichia coli ribosome assembly, is specifically targeted to 23S rRNA in vivo
1Laboratoire de Génétique Moléculaire, CNRS UMR8541, Ecole Normale Supérieure, 46 rue d’Ulm 75230 Paris Cedex 05 and 2Institut de Biologie Physico-chimique, CNRS UPR9073 affiliated with Université Paris 7, 13 rue Pierre et Marie Curie 75005 Paris, France
*To whom correspondence should be addressed. Tel: +33 5 56 99 90 08; Fax: +33 5 56 99 90 15; Email: isabelle.iost{at}ibgc.cnrs.fr
Correspondence may also be addressed to Marc Dreyfus. Tel: +33 1 58 41 51 22; Fax: +33 1 58 41 50 20; Email: marc.dreyfus{at}ibpc.fr
Received July 1, 2009. Revised August 3, 2009. Accepted August 3, 2009.
DEAD-box proteins play specific roles in remodeling RNA or ribonucleoprotein complexes. Yet, in vitro, they generally behave as nonspecific RNA-dependent ATPases, raising the question of what determines their specificity in vivo. SrmB, one of the five Escherichia coli DEAD-box proteins, participates in the assembly of the large ribosomal subunit. Moreover, when overexpressed, it compensates for a mutation in L24, the ribosomal protein (r-protein) thought to initiate assembly. Here, using the tandem affinity purification (TAP) procedure, we show that SrmB forms a complex with r-proteins L4, L24 and a region near the 5'-end of 23S rRNA that binds these proteins. In vitro reconstitution experiments show that the stability of this complex reflects cooperative interactions of SrmB with L4, L24 and rRNA. These observations are consistent with an early role of SrmB in assembly and explain the genetic link between SrmB and L24. Besides its catalytic core, SrmB possesses a nonconserved C-terminal extension that, we show, is not essential for SrmB function and specificity. In this regard, SrmB differs from DbpA, another DEAD-box protein involved in ribosome assembly.
Present addresses: Dmitrii Trubetskoy, CNRS UMR 7087, Hôpital Pitié-Salpêtrière, 83 bd de l'H;ôpital, 75651 Paris Cedex 13, France.
Isabelle Iost, Institut de Biochimie et Génétique Cellulaires, UMR5095 CNRS-Université Victor Segalen Bordeaux 2, 1 rue Camille Saint-Saëns, 33077 Bordeaux Cedex, France.
The authors wish it to be known that, in their opinion, the first two authors should be regarded as joint First Authors.