The Escherichia coli heat shock protein CIpB restores acquired thermotolerance to a cyanobacterial cIpB deletion mutant

In both prokaryotes and eukaryotes, the heat shock protein ClpB functions a s a molecular chaperone and plays a key role in resisting high temperature stress. ClpB is important for the development of thermotolerance in yeast a nd cyanobacteria but apparently not in Escherichia coli. We undertook a com plementation study to investigate whether the ClpB protein from E coli (EcC lpB) differs functionally from its cyanobacterial counterpart in the unicel lular cyanobacterium Synechococcus sp. PCC 7942. The EcClpB protein is 56% identical to its ClpB1 homologue in Synechococcus. A plasmid construct was prepared containing the entire E coli clpB gene under the control of the Sy nechococcus clpB1 promoter. This construct was transformed into a Synechoco ccus clpB1 deletion strain (Delta clpB1) and integrated into a phenotypical ly neutral site of the chromosome. The full-length EcClpB protein (EcClpB-9 3) was induced in the transformed Synechococcus strain during heat shock as well as the smaller protein (EcClpB-79) that arises from a second translat ional start inside the single clpB message. Using cell survival measurement s we show that the EcClpB protein can complement the Synechococcus Delta cl pB1 mutant and restore its ability to develop thermotolerance. We also demo nstrate that both EcClpB-93 and -79 appear to contribute to the degree of a cquired thermotolerance restored to the Synechococcus complementation strai ns.