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PLoS Biol. 2013 Dec;11(12):e1001735. doi: 10.1371/journal.pbio.1001735. Epub 2013 Dec 17.

Heat shock transcription factor σ32 co-opts the signal recognition particle to regulate protein homeostasis in E. coli.

Author information

1
Department of Microbiology and Immunology, University of California at San Francisco, San Francisco, California, United States of America.
2
Institute for Virus Research, Kyoto University, Kyoto, Japan.
3
Department of Biochemistry and Biophysics and Howard Hughes Medical Institute, University of California at San Francisco, San Francisco, California United States of America.
4
Department of Biology, Texas A&M University, College Station, Texas, United States of America.
5
Faculty of Life Sciences, Kyoto Sangyo University, Kyoto, Japan.
6
Department of Microbiology and Immunology, University of California at San Francisco, San Francisco, California, United States of America ; Department of Cell and Tissue Biology, University of California at San Francisco, San Francisco, California, United States.

Abstract

All cells must adapt to rapidly changing conditions. The heat shock response (HSR) is an intracellular signaling pathway that maintains proteostasis (protein folding homeostasis), a process critical for survival in all organisms exposed to heat stress or other conditions that alter the folding of the proteome. Yet despite decades of study, the circuitry described for responding to altered protein status in the best-studied bacterium, E. coli, does not faithfully recapitulate the range of cellular responses in response to this stress. Here, we report the discovery of the missing link. Surprisingly, we found that σ(32), the central transcription factor driving the HSR, must be localized to the membrane rather than dispersed in the cytoplasm as previously assumed. Genetic analyses indicate that σ(32) localization results from a protein targeting reaction facilitated by the signal recognition particle (SRP) and its receptor (SR), which together comprise a conserved protein targeting machine and mediate the cotranslational targeting of inner membrane proteins to the membrane. SRP interacts with σ(32) directly and transports it to the inner membrane. Our results show that σ(32) must be membrane-associated to be properly regulated in response to the protein folding status in the cell, explaining how the HSR integrates information from both the cytoplasm and bacterial cell membrane.

PMID:
24358019
PMCID:
PMC3866087
DOI:
10.1371/journal.pbio.1001735
[Indexed for MEDLINE]
Free PMC Article
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