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Journal of Bacteriology, October 2008, p. 6625-6635, Vol. 190, No. 20
0021-9193/08/$08.00+0     doi:10.1128/JB.00799-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Growth-Promoting and Stress Response Activities of the Bacillus subtilis GTP Binding Protein Obg Are Separable by Mutation{triangledown}

Shrin Kuo,1,{dagger} Borries Demeler,2 and W. G. Haldenwang1*

Departments of Microbiology and Immunology,1 Biochemistry, The University of Texas Health Science Center at San Antonio, San Antonio, Texas 78229-39002

Received 6 June 2008/ Accepted 28 July 2008

Bacillus subtilis Obg is a ribosome-associating GTP binding protein that is needed for growth, sporulation, and induction of the bacterium's general stress regulon (GSR). It is unclear whether the roles of Obg in sporulation and stress responsiveness are direct or a secondary effect of its growth-promoting functions. The present work addresses this question by an analysis of two obg alleles whose phenotypes argue for direct roles for Obg in each process. The first allele [obg(G92D)] encodes a missense change in the protein's highly conserved "obg fold" region. This mutation impairs cell growth and the ability of Obg to associate with ribosomes but fails to block sporulation or the induction of the GSR. The second obg mutation [obg({Delta}22)] replaces the 22-amino-acid carboxy-terminal sequence of Obg with an alternative 26-amino-acid sequence. This Obg variant cofractionates with ribosomes and allows normal growth but blocks sporulation and impairs the induction of the GSR. Additional experiments revealed that the block on sporulation occurs early, preventing the activation of the essential sporulation transcription factor Spo0A, while inhibition of the GSR appears to involve a failure of the protein cascade that normally activates the GSR to effectively catalyze the reactions needed to activate the GSR transcription factor ({sigma}B).

* Corresponding author. Mailing address: Department of Microbiology and Immunology, MSC 7758, The University of Texas Health Science Center at San Antonio, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900. Phone: (210) 567-3957. Fax: (210) 567-6612. E-mail: Haldenwang{at}uthscsa.edu

{triangledown} Published ahead of print on 8 August 2008.

{dagger} Present address: SA Scientific, Ltd., 4919 Golden Quail, San Antonio, TX 78240.

Journal of Bacteriology, October 2008, p. 6625-6635, Vol. 190, No. 20
0021-9193/08/$08.00+0     doi:10.1128/JB.00799-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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