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Journal of Bacteriology, November 2001, p. 6532-6537, Vol. 183, No. 22
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.22.6532-6537.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Involvement of the N Terminus of Ribosomal Protein L11 in Regulation of the RelA Protein of Escherichia coli†

Xiaoming YangDagger and Edward E. Ishiguro*

Department of Biochemistry and Microbiology, University of Victoria, Victoria, British Columbia, Canada V8W 3P6

Received 14 May 2001/Accepted 31 August 2001

Amino acid-deprived rplK (previously known as relC) mutants of Escherichia coli cannot activate (p)ppGpp synthetase I (RelA) and consequently exhibit relaxed phenotypes. The rplK gene encodes ribosomal protein L11, suggesting that L11 is involved in regulating the activity of RelA. To investigate the role of L11 in the stringent response, a derivative of rplK encoding L11 lacking the N-terminal 36 amino acids (designated 'L11) was constructed. Bacteria overexpressing 'L11 exhibited a relaxed phenotype, and this was associated with an inhibition of RelA-dependent (p)ppGpp synthesis during amino acid deprivation. In contrast, bacteria overexpressing normal L11 exhibited a typical stringent response. The overexpressed 'L11 was incorporated into ribosomes and had no effect on the ribosome-binding activity of RelA. By several methods (yeast two-hybrid, affinity blotting, and copurification), no direct interaction was observed between the C-terminal ribosome-binding domain of RelA and L11. To determine whether the proline-rich helix of L11 was involved in RelA regulation, the Pro-22 residue was replaced with Leu by site-directed mutagenesis. The overexpression of the Leu-22 mutant derivative of L11 resulted in a relaxed phenotype. These results indicate that the proline-rich helix in the N terminus of L11 is involved in regulating the activity of RelA.

* Corresponding author. Mailing address: Department of Biochemistry and Microbiology, University of Victoria, P.O. Box 3055, Victoria, British Columbia, Canada V8W 3P6. Phone: (250) 721 7077. Fax: (250) 721 8855. E-mail: eishuv{at}uvvm.uvic.ca.

dagger We dedicate this paper to the memory of our friend and colleague, Alistair T. Matheson, who passed away on 18 May 2001.

Dagger Present address: Department of Genetics, Yale University, New Haven, CT 06510-3206.

Journal of Bacteriology, November 2001, p. 6532-6537, Vol. 183, No. 22
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.22.6532-6537.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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