Abstract
In contrast to the E.coli genome in which only one groEL gene is present, there are two groEL genes, groEL1 and groEL2, in the cyanobacterial genome. Expression of the groEL1 gene may be negatively regulated by the CIRCE/HrcA system since CIRCE is located around transcriptional start sites of the cyanobacterial groESL1 operons. CIRCE has been shown to act as a negative cis-element of grpE/dnaK/dnaJ and/or groE operons. In contrast with groEL1, groEL2 from some cyanobacteria such as Thermosynechococcus elongatus lack CIRCE.
In the present study, we studied expression and function of GroEL2 from T.elongatus. Both groEL genes were induced by heat shock. However, only groEL2 was induced by cold treatment. In order to elucidate the GroEL2 function, the gene was disrupted by gene targeting. The mutant was sensitive to high temperature, low temperature, and high irradiance, indicating that GroEL2 plays important roles under various stress conditions.
