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Two different mechanisms are involved in the heat‐shock regulation of chaperonin gene expression in Bradyrhizobium japonicum
Author(s) -
Babst Markus,
Hennecke Hauke,
Fischer HansMartin
Publication year - 1996
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.1365-2958.1996.438968.x
Subject(s) - groel , biology , chaperonin , heat shock protein , bacillus subtilis , psychological repression , heat shock , bradyrhizobium japonicum , groes , genetics , gene , transcription (linguistics) , lac operon , gene expression , microbiology and biotechnology , escherichia coli , bacteria , rhizobiaceae , linguistics , philosophy , symbiosis
Heat‐shock regulation was detected for three out of the five members of the groESL multigene family in Bradyrhizobium japonicum . The results uncovered the simultaneous presence of two distinct heat‐shock control systems which so far have not been reported to co‐exist in a single prokaryotic organism. The first system concerns groESL 1 whose transcription is controlled in a σ 32 ‐dependent manner similar to that known from work done with Escherichia coli . Heat‐shock control of groESL 4 is mediated by the second system, which is characterized by an inverted‐repeat DNA structure originally described as a heat‐shock regulatory element (CIRCE) in Bacillus subtilis . This element represses expression of groESL 4 under non‐stress conditions, as inferred from the increased expression of a groESL 4 ′–′ lacZ fusion suffering a 4 bp deletion within the CIRCE element. The two control systems clearly differ with respect to the temperature dependence and the kinetics of the heat‐shock response, and they also respond differently to the stress signal elicited by incorporation of the amino acid analogue p ‐F‐phenylalanine into cellular protein. Knock‐out mutations in groEL 4 resulted in an increased expression of groESL 4 , suggesting that repression via CIRCE depends, itself, upon the cellular level of GroEL 4 protein.