CLONING OF THE 2ND ADENYLATE-CYCLASE GENE (CYA2) FROM RHIZOBIUM-MELILOTI F34 - SEQUENCE SIMILARITY TO EUKARYOTIC CYCLASES

A second adenylate cyclase (cya2) gene was isolated from a Rhizobium m eliloti F34 gene bank. Complemented E. coli Delta cya mutants were cap able of utilizing a number of, but not all, carbon sources known to be regulated by cAMP. DNA hybridization studies showed cya2 to be unique to R. meliloti strains. The cya2 nucleotide sequence was determined a nd found to encode a protein of 363 amino acids. Residues were identif ied within the C-terminal domain which are conserved in both eukaryoti c adenylate and guanylate cyclases, including a putative ATP binding s ite. Similiar residues were also found in the prokaryotic R. meliloti Cya1 protein. A R. meliloti cya1/cya2 double mutant was constructed an d characterized; however, cAMP production was still observed in this s train indicating the presence of a third cya gene.