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Journal of Bacteriology, April 2009, p. 2485-2492, Vol. 191, No. 8
0021-9193/09/$08.00+0     doi:10.1128/JB.01734-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Novel trans-Acting Bacillus subtilis glnA Mutations That Derepress glnRA Expression{triangledown}

Susan H. Fisher* and Lewis V. Wray Jr.

Department of Microbiology, Boston University School of Medicine, Boston, Massachusetts 02118

Received 11 December 2008/ Accepted 10 February 2009

Bacillus subtilis contains two nitrogen transcription factors, GlnR and TnrA. The activities of GlnR and TnrA are regulated by direct protein-protein interactions with the feedback-inhibited form of glutamine synthetase (GS). To look for other factors involved in regulating GlnR activity, we isolated mutants with constitutive glnRA expression (GlnC). The twenty-seven GlnC mutants isolated in this mutant screen all contained mutations tightly linked to the glnRA operon which encodes GlnR (glnR) and GS (glnA). Four GlnC mutants contained mutations in the glnR gene that most likely impair the ability of GlnR to bind DNA. Three other GlnC mutants contained novel glnA mutations (S55F, V173I, and L174F). GlnR regulation was completely relieved in the three glnA mutants, while only modest defects in TnrA regulation were observed. In vitro enzymatic assays showed that the purified S55F mutant enzyme was catalytically defective while the V173I and L174F enzymes were highly resistant to feedback inhibition. The V173I and L174F GS proteins were found to require higher glutamine concentrations than the wild-type GS to regulate the DNA-binding activities of GlnR and TnrA in vitro. These results are consistent with a model where feedback-inhibited GS is the only cellular factor involved in regulating the activity of GlnR in B. subtilis.

* Corresponding author. Mailing address: Department of Microbiology, Boston University School of Medicine, 72 East Concord Street, Boston, MA 02118-2526. Phone: (617) 638-5498. Fax: (617) 638-4286. E-mail: shfisher{at}bu.edu

{triangledown} Published ahead of print on 20 February 2009.

Journal of Bacteriology, April 2009, p. 2485-2492, Vol. 191, No. 8
0021-9193/09/$08.00+0     doi:10.1128/JB.01734-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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