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Journal of Bacteriology, October 2006, p. 6757-6770, Vol. 188, No. 19
0021-9193/06/$08.00+0     doi:10.1128/JB.00444-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.

The Escherichia coli GTPase CgtAE Is Involved in Late Steps of Large Ribosome Assembly{dagger}

Mengxi Jiang,1 Kaustuv Datta,1 Angela Walker,2 John Strahler,2 Pia Bagamasbad,1 Philip C. Andrews,2 and Janine R. Maddock1*

Department of Molecular, Cellular and Developmental Biology,1 Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 481092

Received 30 March 2006/ Accepted 31 May 2006

The bacterial ribosome is an extremely complicated macromolecular complex the in vivo biogenesis of which is poorly understood. Although several bona fide assembly factors have been identified, their precise functions and temporal relationships are not clearly defined. Here we describe the involvement of an Escherichia coli GTPase, CgtAE, in late steps of large ribosomal subunit biogenesis. CgtAE belongs to the Obg/CgtA GTPase subfamily, whose highly conserved members are predominantly involved in ribosome function. Mutations in CgtAE cause both polysome and rRNA processing defects; small- and large-subunit precursor rRNAs accumulate in a cgtAE mutant. In this study we apply a new semiquantitative proteomic approach to show that CgtAE is required for optimal incorporation of certain late-assembly ribosomal proteins into the large ribosomal subunit. Moreover, we demonstrate the interaction with the 50S ribosomal subunits of specific nonribosomal proteins (including heretofore uncharacterized proteins) and define possible temporal relationships between these proteins and CgtAE. We also show that purified CgtAE associates with purified ribosomal particles in the GTP-bound form. Finally, CgtAE cofractionates with the mature 50S but not with intermediate particles accumulated in other large ribosome assembly mutants.

* Corresponding author. Mailing address: Department of Molecular, Cellular and Developmental Biology, University of Michigan, 830 North University, Ann Arbor, MI 48109-1048. Phone: (734) 936-8068. Fax: (734) 647-0884. E-mail: maddock{at}umich.edu.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, October 2006, p. 6757-6770, Vol. 188, No. 19
0021-9193/06/$08.00+0     doi:10.1128/JB.00444-06
Copyright © 2006, American Society for Microbiology. All Rights Reserved.



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