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J. Bacteriol. doi:10.1128/JB.01193-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Interactions of an essential Bacillus subtilis GTPase, YsxC, with ribosomes

Institut de Biologie Structurale, UMR 5075 Université Joseph Fourier/CEA/CNRS, 41 rue Jules Horowitz 38027 Grenoble Cedex 1, France; CEA, DSV, iRTSV, Laboratoire d'Etude de la Dynamique des Protéomes, Grenoble, F-38054, France; INSERM, U880, Grenoble, F-38054, France; Université Joseph Fourier, Grenoble, F-38054, France; Department of Microbiology and Molecular Genetics, Michigan State University, East Lansing, MI 48824, USA

^* To whom correspondence should be addressed. Email: catherine.wicker-planquart{at}ibs.fr.

	Abstract

YsxC is a small GTPase of Bacillus subtilis with essential but still unknown function, yet recent work have suggested that it might be involved in ribosomes biogenesis. Here, purified YsxC overexpressed in E. coli was found to be partly associated with high molecular weight material, most likely rRNA, thus eluting from gel filtration as a large complex. In addition, purification of ribosomes from an E. coli strain overexpressing YsxC allowed the co-purification of the YsxC protein. Purified YsxC was shown to bind preferentially to the 50S subunit of B. subtilis ribosomes and this interaction was modulated by nucleotides, being stronger in the presence of a non-hydrolysable GTP analogue as opposed to GTP. Far Western-blotting analysis performed with (His)₆-YsxC and ribosomal proteins separated by SDS-PAGE showed that YsxC interacted with at least four ribosomal proteins from the 50S subunit. Two of these putative protein partners were identified by mass spectrometry as L1 and L3, while the third reactive band in the 1-D gel contained L6 and L10. The fourth band that reacted with YsxC contained a mixture of three proteins, L7/L12, L23 and L27, suggesting that at least one of them binds to YsxC. Co-immobilization assays confirmed that L1, L6 and L7/L12 interact with YsxC. Altogether, these results suggest that YsxC plays a role in ribosome assembly.