Expression of the groESL operon is cell-cycle controlled in Caulobacter crescentus

The Caulobacter crescentus groESL operon was cloned, sequenced and found to be homologous to previously described groES and groEL genes and proteins. The size of the groESL-specific transcript (2.3 kb) suggested that groES and groEL of C. crescentus are organized in a bicistronic operon. Heat-shock induction of groESL mRNA is not transient, high levels of the transcript can be observed after 2 h at 40 degrees C. Primer extension experiments showed that transcription initiated at two sites. Only the start site closer to the groES coding region was highly induced during heat shock. The promoter corresponding to the heat-shock-inducible transcript has -10 and -35 regions very similar to Escherichia coli sigma 32 promoters. At normal temperatures, transcription of the groESL operon is cell-cycle controlled and both transcripts increase co-ordinately in pre-divisional cells. Transcription fusions with a lacZ reporter gene and deletions within the promoter region of the groESL operon have shown that no sequences upstream of the heat-shock promoter 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 several heat-shock genes of other bacteria, may play a role in cell-cycle control of C. crescentus groESL expression.