Two different mechanisms are involved in the heat-shock regulation of chaperonin gene expression in Bradyrhizobium japonicum.
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 groESL1 whose transcription is controlled in a sigma32-dependent manner similar to that known from work done with Escherichia coli. Heat-shock control of groESL4 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 groESL4 under non-stress conditions, as inferred from the increased expression of a groESL4'-'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 groEL4 resulted in an increased expression of groESL4, suggesting that repression via CIRCE depends, itself, upon the cellular level of GroEL4 protein.
Babst
M
M
Mikrobiologisches Institut, Eidgenossische Technische Hochschule, Zurich, Switzerland.
Hennecke
H
H
Fischer
H M
HM
D001483:Base Sequence; D018835:Chaperonin 10 / Q000235:genetics*; D018834:Chaperonin 60 / Q000235:genetics; D002874:Chromosome Mapping; D004926:Escherichia coli / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D006360:Heat-Shock Proteins / Q000235:genetics / Q000302:isolation & purification; D018869:Heat-Shock Response / Q000235:genetics*; D008969:Molecular Sequence Data; D009876:Operon / Q000235:genetics; D011401:Promoter Regions, Genetic; D011994:Recombinant Proteins; D012230:Rhizobiaceae / Q000235:genetics*; D017385:Sequence Homology; D012808:Sigma Factor / Q000235:genetics / Q000302:isolation & purification; D014157:Transcription Factors; D014158:Transcription, Genetic
D018835:Chaperonin 10; D018834:Chaperonin 60; D006360:Heat-Shock Proteins; D011994:Recombinant Proteins; D012808:Sigma Factor; D014157:Transcription Factors; C069774:heat-shock sigma factor 32