A PUTATIVE TRANSCRIPTIONAL ACTIVATOR OF THE CRP FNR FAMILY FROM THE MARINE CYANOBACTERIUM SYNECHOCOCCUS SP WH7803/

Sequence analysis immediately downstream (3') of a genomic region of S ynechococcus sp. WH7803, encoding a periplasmic phosphate-binding prot ein (PstS), revealed an open reading frame encoding a protein of 224 a mino acids. The protein exhibited considerable sequence similarity to a family of bacterial transcriptional activators that includes Crp and Fnr and consequently the ORF is designated ptrA (putative transcripti onal activator). Upstream of ptrA a 18 nucleotide sequence representin g a putative Pho box was found. Homologues of the ptrA gene were detec ted in several other phycoerythrin-containing marine Synechococcus str ains. This represents the third cyanobacterial member of this class of DNA-binding protein to be described and the first such homologue in t he ecologically important marine Synechococcus group. The location of ptrA immediately downstream from pstS may implicate this protein in gl obal phosphate regulation.