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Journal of Bacteriology, July 2005, p. 4739-4751, Vol. 187, No. 14
0021-9193/05/$08.00+0     doi:10.1128/JB.187.14.4739-4751.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Analysis of the Escherichia coli Alp Phenotype: Heat Shock Induction in ssrA Mutants

Hussain Munavar,2,{dagger} YanNing Zhou,1,{dagger} and Susan Gottesman1*

Bldg. 37, Rm. 5132, Laboratory of Molecular Biology, National Cancer Institute, Bethesda, Maryland 20892-4255,1 Department of Molecular Biology, School of Biological Sciences, Centre for Excellence in Genomic Sciences, Madurai Kamaraj University, Madurai 625021, India2

Received 1 February 2005/ Accepted 4 April 2005

The major phenotypes of lon mutations, UV sensitivity and overproduction of capsule, are due to the stabilization of two substrates, SulA and RcsA. Inactivation of transfer mRNA (tmRNA) (encoded by ssrA), coupled with a multicopy kanamycin resistance determinant, suppressed both lon phenotypes and restored the rapid degradation of SulA. This novel protease activity was named Alp but was never identified further. We report here the identification, mapping, and characterization of a chromosomal mutation, faa (for function affecting Alp), that leads to full suppression of a {Delta}lon ssrA::cat host and thus bypasses the requirement for multicopy Kanr; faa and ssrA mutants are additive in their ability to suppress lon mutants. The faa mutation was mapped to the C terminus of dnaJ(G232); dnaJ null mutants have similar effects. The identification of a lon suppressor in dnaJ suggested the possible involvement of heat shock. We find that ssrA mutants alone significantly induce the heat shock response. The suppression of UV sensitivity, both in the original Alp strain and in faa mutants, is reversed by mutations in clpY, encoding a subunit of the heat shock-induced ClpYQ protease that is known to degrade SulA. However, capsule synthesis is not restored by clpY mutants, probably because less RcsA accumulates in the Alp strain and because the RcsA that does accumulate is inactive. Both ssrA effects are partially relieved by ssrA derivatives encoding protease-resistant tags, implicating ribosome stalling as the primary defect. Thus, ssrA and faa each suppress two lon mutant phenotypes but by somewhat different mechanisms, with heat shock induction playing a major role.

* Corresponding author. Mailing address: Bldg. 37, Rm. 5132, Laboratory of Molecular Biology, National Cancer Institute, Bethesda, MD 20892-4255. Phone: (301) 496-3524. Fax: (301) 496-3875. E-mail: susang{at}helix.nih.gov.

{dagger} Both authors contributed equally to this work.

Journal of Bacteriology, July 2005, p. 4739-4751, Vol. 187, No. 14
0021-9193/05/$08.00+0     doi:10.1128/JB.187.14.4739-4751.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

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