Abstract
We have previously identified three dnaK homologues ( dnaK1, dnaK2 and dnaK3 ) in cyanobacterium Synechococcus sp. PCC7942. DnaK2 and DnaK3 are essential for normal growth, but only DnaK3 has been quantitatively associated with the thylakoid membrane. Among them, only DnaK2 exhibited heat shock response. Thus we speculate that the expression of these dnaK genes are regulated differently.
Here, we show the results of our analysis using dnaK-lacZ fusion, RNA blot hybridization and transcription start sites analysis of dnaK2, under various stress conditions. Exposure to high light and salt stress resulted in dnaK2 induction, but not in dnaK1 and dnaK3. Furthermore, we also observed a multi-step induction but delayed response only during salt stress. 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.
