Nucleotide sequence of plasmid pAQ1 of marine cyanobacterium Synechococcus sp. PCC7002.

We have determined the complete nucleotide sequence of pAQ1, the smallest plasmid of the unicellular marine cyanobacterium Synechococcus sp. PCC7002. The plasmid consists of 4,809 bp and has at least four open reading frames that potentially encode polypeptides of 50 or more amino acids. We found that a palindromic element, the core sequence of which is G(G/A)CGATCGCC, is over-represented not only in plasmid pAQ1 but also in the accumulated cyanobacterial genomic sequences from Synechococcus sp. PCC6301, PCC7002, PCC7942, vulcanus and Synechocystis sp. PCC6803 within GenBank and EMBL databases. It suggests that this sequence might mediate gene rearrangement, thus increasing genetic diversity, since recombination events are frequent in cyanobacteria.