Chaperonin Genes of theSynechocystisPCC 6803 Are Differentially Regulated under Light–Dark Transition during Heat Stress

Transcriptional startpoints of the two heat inducible chaperonin genes ofSynechocystisPCC 6803 were mapped within the conservative CIRCE element and proved to be identical irrespective of the temperature treatment. Finding of an ORF encoding for a potential CIRCE binding repressor (HrcA) further suggests that bothgroEL-analogs are regulated in a CIRCE-dependent manner. In contrast to the expectations, the chaperonin twins are differentially expressed under light–dark transition during heat stress. Not the lightper se,but rather the photosynthetic electron transport appears to be accountable for the regulatory differences. Our findings support the hypothesis that multiple chaperonins play different physiological roles under stress conditions.