EXPRESSION OF THE GROESL OPERON IS CELL-CYCLE CONTROLLED IN CAULOBACTER-CRESCENTUS

The Caulobacter crescentus groESL operon was cloned, sequenced and fou nd to be homologous to previously described groES and groEL genes and proteins. The size of the groESL-specific transcript (2.3 kb) suggeste d that groES and groEL of C. crescentus are organized in a bicistronic operon. Heat-shock induction of groESL mRNA is not transient, high le vels of the transcript can be observed after 2 h at 40 degrees C. Prim er extension experiments showed that transcription initiated at two si tes. Only the start site closer to the groES coding region was highly induced during heat shock. The promoter corresponding to the heatshock -inducible transcript has -10 and -35 regions very similar to Escheric hia coli sigma(32) promoters. At normal temperatures, transcription of the groESL operon is cell-cycle controlled and both transcripts incre ase co-ordinately in pre-divisional cells. Transcription fusions with a lacZ reporter gene and deletions within the promoter region of the g roESL operon have shown that no sequences upstream of the heat-shock p romoter are necessary for temporal control. An 11 bp inverted repeat, located between the heat-shock promoter and the translation start site of groES and very similar to inverted repeats found in front of sever al heat-shock genes of other bacteria, may play a role in cell-cycle c ontrol of C. crescentus groESL expression.