The groESL operon of Agrobacterium tumefaciens: evidence for heat shock-dependent mRNA cleavage.

The heat shock response of the groESL operon of Agrobacterium tumefaciens was studied at the RNA level. The operon was found to be activated under heat shock conditions and transcribed as a polycistronic mRNA that contains the groES and groEL genes. After activation, the polycistronic mRNA appeared to be cleaved between the groES and groEL genes and formed two monocistronic mRNAs. The groES cleavage product appeared to be unstable and subjected to degradation, while the groEL cleavage product appeared to be stable and became the major mRNA representing the groESL operon after long periods of growth at a high temperature. The polycistronic mRNA containing the groES and groEL genes was the major mRNA representing the groESL operon at a low temperature, and it reappeared when the cells were returned to the lower growth temperature after heat shock induction. These findings indicate that the cleavage event is part of the heat shock regulation of the groESL operon in A. tumefaciens.     

The groESL operon of the halophilic lactic acid bacterium Tetragenococcus halophila

The groESL operon of the halophilic lactic acid bacterium Tetragenococcus halophila was cloned by a PCR-based method. The molecular masses of GroES and GroEL proteins were calculated to be 10,153 and 56,893 Da, respectively. The amount of groESL mRNA was increased 3.8-fold by heat shock (45 degrees C), and 4-fold by high NaCl (3-4 M). The Bacillus subtilis sigmaA-like constitutive promoter existed in front of groES, and was used under both normal and stress (heat shock and high salinity) conditions.     

Expression and control of an operon from an intracellular symbiont which is homologous to the groE operon.

Members of the genus Buchnera are intracellular symbionts harbored by the aphid bacteriocyte which selectively synthesize symbionin, a homolog of the Escherichia coli GroEL protein, in vivo. Symbionin and SymS, a GroES homolog, are encoded in the symSL operon. Northern blotting and primer extension analyses revealed that the symSL operon invariably gives rise to a bicistronic mRNA under the control of a heat shock promoter, though the amount of the symSL mRNA in the isolated symbiont did not increase in response to heat shock. The sigma32 protein that recognizes the heat shock promoter in E. coli was scarcely detected in Buchnera cells even after heat shock. Although the functionally essential regions of the Buchnera sigma32 protein were well conserved, the Buchnera rpoH gene did not complement an E. coli delta rpoH mutant. On the one hand, the A-T evolutionary pressure imposed on the Buchnera genome may have not only decreased the activity of its sigma32 but also ruined the nucleotide sequences necessary for the expression of rpoH; on the other hand, it may have facilitated expression of the symSL operon without activation by sigma32.