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Downregulation of the heat shock response is independent of DnaK and σ 32 levels in Caulobacter crescentus
Author(s) -
Da Silva Antonio C.A.,
Simão Rita C.G.,
Susin Michelle F.,
Baldini Regina L.,
Avedissian Marcelo,
Gomes Suely L.
Publication year - 2003
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1046/j.1365-2958.2003.03581.x
Subject(s) - sigma factor , caulobacter crescentus , biology , groel , groes , heat shock protein , heat shock , rpos , microbiology and biotechnology , gene expression , transcription (linguistics) , chaperone (clinical) , downregulation and upregulation , heat shock factor , rna polymerase , gene , promoter , hsp70 , rna , biochemistry , cell cycle , escherichia coli , medicine , linguistics , philosophy , pathology
Summary Expression of heat shock genes in Gram‐negative proteobacteria is positively modulated by the transcriptional regulator RpoH, the σ 32 subunit of RNA polymerase (RNAP). In this study we investigated the chaperones DnaK/DnaJ and GroES/GroEL as possible modulators of the heat response in Caulobacter crescentus . We have shown that cells overexpressing DnaK show poor induction of heat shock protein (HSP) synthesis, even though σ 32 levels present a normal transient increase upon heat stress. On the other hand, depletion of DnaK led to higher levels of σ 32 and increased transcription of HSP genes, at normal growth temperature. In contrast, changes in the amount of GroES/EL had little effect on σ 32 levels and HSP gene transcription. Despite the strong effect of DnaK levels on the induction phase of the heat shock response, downregulation of HSP synthesis was not affected by changes in the amount this chaperone. Thus, we propose that competition between σ 32 and σ 73 , the major sigma factor, for the core RNAP could be the most important factor controlling the shut‐off of HSP synthesis during recovery phase. In agreement with this hypothesis, we have shown that expression of σ 73 gene is heat shock inducible.