UNIQUE ORGANIZATION OF THE DNAA REGION FROM PROCHLOROCOCCUS-MARINUS CCMP1375, A MARINE CYANOBACTERIUM

In order to study DNA replication control elements in cyanobacteria we cloned and sequenced the dnaA gene from the marine cyanobacterium Pro chlorococcus marinus. The dnaA gene is ubiquitous among bacteria and e ncodes the DNA replication initiation factor DnaA. The deduced amino a cid sequence of the P. marinus DnaA protein shows highest similarity t o the DnaA protein from the freshwater cyanobacterium Synechocystis sp . PCC6803. Using a solid-phase DNA binding assay we demonstrated that both cyanobacterial DnaA proteins specifically recognize chromosomal o rigins, oriC, of Escherichia coli and Bacillus subtilis in vitro. The genetic environment of dnaA is not conserved between the two cyanobact eria. Upstream of the P. murinus dnaA gene we identified a gene encodi ng a putative ATP-binding cassette (ABC) transport protein. The gor ge ne encoding glutathione reductase lies downstream of dnaA. Comparison of the genetic structure of dnaA regions from 15 representative bacter ia shows that the pattern of genes flanking dnaA is not universally co nserved among them.