Molecular cloning of the genes encoding two chaperone proteins of the cyanobacterium Synechocystis sp. PCC 6803.

Molecular chaperones help other proteins in their correct folding and assembly. We have cloned the genes, cpn60 and dnaK, which encode proteins belonging to the chaperonin-60 and the 70-kDa heat shock protein families from the transformable cyanobacterium Synechocystis sp. PCC 6803. These genes are present in single copies in the genome, and the major transcripts for each gene are monocistronic. Comparison of deduced amino acid sequences reveals that cyanobacterial chaperonin-60 is equally homologous to bacterial and plant chaperonin-60 proteins while the product of dnaK is more similar to its bacterial homologues than to its eukaryotic counterparts. The DNA fragments sequenced in these studies also contain five other open reading frames. One of them, ORF60-5, encodes a protein whose deduced amino acid sequence shows remarkable similarity to those of a family of peripheral membrane proteins involved in metabolite transport in bacteria. The transcript levels of dnaK and cpn60 of Synechocystis sp. PCC 6803 increase in response to stress conditions such as heat shock, ultraviolet exposure, and oxidative stress. This is one of the first examples of cyanobacterial gene expression being regulated by environmental stresses.