Abstract
We have previously reporterted that one of the three dnaK homologues ( dnaK1, dnaK2 and dnaK3 ) in cyanobacterium Synechococcus sp. PCC7942, dnaK2, was found to be induced during heat shock, high light and salt stresses. Primer extension mapping revealed several transcription start site of dnaK2 while no sequence homology with the Escherichia coli sigma-70-like or heat shock promoters was observed. It was suggested that other factors might relate to heat response of the dnaK2 gene.Transcriptional reporter assay using thermostable beta-galactosidase gene, bgaB, revealed that, in addition to the upstream regulatory sequence, the region corresponding to the N-terminal coding sequence was required for substantial expression and heat induction of the dnaK2 gene. Moreover, the 20bp sequence element in the upstream region was highly conserved among cyanobacterial dnaK and this element was also necessary for heat induction of the dnaK2 gene.
