Summary: We have cloned and sequenced a gene of the cyanobacterium sp. strain PCC 6803 named (encoding drug sensory protein A; DspA), mutations in which result in cross-resistance to the herbicides difunon and diuron, as well as to the calmodulin antagonists chlorpromazine and trifluoperazine. The gene encodes a polypeptide of 663 amino acids with a predicted molecular mass of 74·5 kDa. The molecular nature of two mutations in the gene leading to the cross-resistance has been determined. Targeted mutagenesis of the gene was performed using a kanamycin-resistance gene cartridge. Resulting mutant strains were checked for resistance to difunon and chlorpromazine and showed cross-resistance to both agents. The C-terminal portion of the deduced amino acid sequence of DspA shares significant similarity with the conserved region of histidine protein kinases (HPKs). Hydrophobicity analysis of the amino acid sequence of DspA indicated the existence of two hydrophobic regions in the N-terminal portion that are characteristic of the bacterial sensory HPK family. We suggest that protein DspA is a HPK involved in chemical sensing.


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