Open AccessDynamic interplay between antagonistic pathways controlling the σ 32 level in Escherichia coli
Author(s) -
Miyo Terao Morita,
Masaaki Kanemori,
Hideki Yanagi,
Takashi Yura
Publication year - 2000
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.080495197
Subject(s) - chaperone (clinical) , escherichia coli , translation (biology) , protein biosynthesis , heat shock , heat shock protein , biophysics , biology , chemistry , polysome , microbiology and biotechnology , messenger rna , biochemistry , gene , rna , ribosome , medicine , pathology
The heat-shock response inEscherichia coli depends primarily on the transient increase in the cellular level of heat-shock sigma factor σ32 encoded by therpoH gene, which results from both enhanced synthesis and transient stabilization of normally unstable σ32 . Heat-induced synthesis of σ32 was previously shown to occur at the translation level by melting the mRNA secondary structure formed within the 5′ coding sequence ofrpoH including the translation initiation region. The subsequent decrease in the σ32 level during the adaptation phase has been thought to involve both shutoff of synthesis (translation) and destabilization of σ32 -mediated by the DnaK–DnaJ chaperones, although direct evidence for translational repression was lacking. We now show that the heat-induced synthesis of σ32 does not shut off at the translation level by using a reporter system involving translational coupling. Furthermore, the apparent shutoff was not observed when the synthesis rate was determined by a very short pulse labeling (15 s). Examination of σ32 stability at 10 min after shift from 30 to 42°C revealed more extreme instability (t 1/2 =20 s) than had previously been thought. Thus, the dynamic change in σ32 stability during the heat-shock response largely accounts for the apparent shutoff of σ32 synthesis observed with a longer pulse. These results suggest a mechanism for maintaining the intricate balance between the antagonistic pathways: therpoH translation as determined primarily by ambient temperature and the turnover of σ32 as modulated by the chaperone (and presumably protease)-mediated autogenous control.