The Spirulina platensis adenylate cyclase gene, cyaC, encodes a novel signal transduction protein

A cyaC gene encoding an adenylate cyclase of the filamentous cyanobacterium Spirulina platensis was se-quenced. The predicted amino acid sequence of the C-ter-minal region of cyaC is similar to the catalytic domains of adenylate cyclases in other cyanobacteria and eukaryotes. The sequences of other regions are similar to those of proteins consisting of the bacterial two-component signal transduction system: the sensory kinase and the response regulator. The predicted gene product of cyaC contains, from the N-terminal end, a receiver domain of the response regulator protein (Rl), a domain similar to the ETR1 of Arabi-dopsis thaliana, a transmitter domain of the sensory kinase protein, a receiver domain of the response regulator protein (R2), and a catalytic domain of adenylate cyclase. The cyaC gene was expressed as an affinity-tagged protein in Escherichia coli, and the recombinant protein was purified. The purified protein had adenylate cyclase activity which was activated by Mn2+. The results of Western blotting using an anti-CyaC antiserum and the S. platensis cell extract confirmed that cyaC gene is expressed in S. platensis