Cloning of a sensory-kinase-encoding gene that belongs to the two-component regulatory family from the cyanobacterium Synechococcus sp. PCC7942.

A screening method employing Escherichia coli was adopted to clone a sensory-kinase (SK)-encoding gene directly from a phylogenetically distant species, the phototrophic cyanobacterium Synechococcus sp. PCC7942. From the Synechococcus chromosomal DNA, we searched for DNA clones which are able to complement phenotypically not only an E. coli envZ mutant for the expression of ompC, but also an E. coli phoR/creC mutant for the expression of alkaline phosphatase. These E. coli genes are known to encode SK. A 0.75-kb DNA fragment was thus cloned under the control of the E. coli lac promoter carried on an E. coli plasmid vector. A larger DNA fragment encompassing an entire open reading frame was then cloned and its complete nucleotide (nt) sequence determined. The nt sequence corresponds to a gene that encodes a 43,280-Da protein of 387 amino acids with a high degree of homology to the bacterial SK. Thus, we succeeded in cloning a SK-encoding gene, which most likely functions in signal transduction in Synechococcus sp. PCC7942. Hence, the gene was designated sasA (Synechococcus adaptive-response SK A). The purified SasA protein was demonstrated in vitro to undergo autophosphorylation.