JB
Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
This Article
Right arrow Full Text
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Copyright Information
Right arrow Books from ASM Press
Right arrow MicrobeWorld
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Bernstein, H. D.
Right arrow Articles by Hyndman, J. B.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Bernstein, H. D.
Right arrow Articles by Hyndman, J. B.

Journal of Bacteriology, April 2001, p. 2187-2197, Vol. 183, No. 7
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.7.2187-2197.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Physiological Basis for Conservation of the Signal Recognition Particle Targeting Pathway in Escherichia coli

Harris D. Bernstein* and Janine B. Hyndman

Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-1810

Received 2 November 2000/Accepted 5 January 2001

The Escherichia coli signal recognition particle (SRP) is a ribonucleoprotein complex that targets nascent inner membrane proteins (IMPs) to transport sites in the inner membrane (IM). Since SRP depletion only partially inhibits IMP insertion under some growth conditions, however, it is not clear why the particle is absolutely essential for viability. Insights into this question emerged from experiments in which we analyzed the physiological consequences of reducing the intracellular concentration of SRP below the wild-type level. We found that even moderate SRP deficiencies that have little effect on cell growth led to the induction of a heat shock response. Genetic manipulations that suppress the heat shock response were lethal in SRP-deficient cells, indicating that the elevated synthesis of heat shock proteins plays an important role in maintaining cell viability. Although it is conceivable that the heat shock response serves to increase the capacity of cells to target IMPs via chaperone-based mechanisms, SRP-deficient cells did not show an increased dependence on either GroEL or DnaK. By contrast, the heat shock-regulated proteases Lon and ClpQ became essential for viability when SRP levels were reduced. These results suggest that the heat shock response protects SRP-deficient cells by increasing their capacity to degrade mislocalized IMPs. Consistent with this notion, a model IMP that was mislocalized in the cytoplasm as the result of SRP depletion appeared to be more stable in a Delta lon Delta clpQ strain than in control cells. Taken together, the data provide direct evidence that SRP is essential in E. coli and possibly conserved throughout prokaryotic evolution as well partly because efficient IMP targeting prevents a toxic accumulation of aggregated proteins in the cytoplasm.


* Corresponding author. Mailing address: National Institutes of Health, Building 10, Room 9D-20, Bethesda, MD 20892-1810. Phone: (301) 402-4770. Fax: (301) 402-0387. E-mail: harris_bernstein{at}nih.gov.


Journal of Bacteriology, April 2001, p. 2187-2197, Vol. 183, No. 7
0021-9193/01/$04.00+0   DOI: 10.1128/JB.183.7.2187-2197.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.



This article has been cited by other articles:




Home Help [Feedback] [For Subscribers] [Archive] [Search] [Contents]
Appl. Environ. Microbiol. Infect. Immun. Eukaryot. Cell
Mol. Cell. Biol. J. Virol. Microbiol. Mol. Biol. Rev.
ALL ASM JOURNALS

Copyright © 2001 by the American Society for Microbiology. All rights reserved.