REGULATION OF THE CAULOBACTER-CRESCENTUS DNAKJ OPERON

The bacterial heat shock proteins DnaK and DnaJ are members of a class of molecular chaperones that are required for a wide variety of cellu lar functions at normal growth temperatures, In Caulobacter crescentus , the expression of the dnaKJ operon is regulated both temporally duri ng the normal cell cycle and by heat shock Analysis of deletions and b ase substitutions in the 5' region of the operon established the prese nce of two functional promoters: a heat shock-inducible promoter, P1, with characteristics of a sigma(32) promoter, and an adjacent sigma(70 )-like promoter, P2, Transcription initiating at the sigma(70)-like pr omoter is under strict temporal control, whereas transcription initiat ing at the heal shock promoter at 30 degrees C is not, Transcription o f dnaKJ occurs during a short period in the cell cycle, concomitant wi th the onset of DNA replication, Deletions in the 5' region have also revealed that all cis-acting sites required for temporal control of tr anscription reside within 50 bases of the P2 start site, Transcripts i nitiating from either the P1 or the P2 promoter have an RNA leader seq uence with a high probability of forming an extensive secondary struct ure, Deletion of this leader sequence resulted in an increased rate of expression in both transcriptional and translational fusions, Althoug h the temporal control of expression at physiological temperatures is not affected by the presence or absence of the leader sequence, change s in mRNA secondary structure may contribute to the modulation of DnaK and DnaJ levels at normal temperatures and during heat shock.