Library screening of sequences that replicate autonomously in cyanobacterial cell.

While the replication initiation start site has been identified in Synechococcus elongatus PCC 7942, it is not yet identified in Synechocystis sp. PCC 6803. To gain new insights into the regions of high replication activity in the cyanobacteria Synechocystis sp. PCC 6803 and Synechococcus elongatus PCC 7942, genomic library has been constructed by the cloning to E. coli vector. These libraries were used for the transformation of Synechocystis or Synechococcus, and DNA extract from transformants were pooled. To retrieve plasmids that existed independently without chromosomal integration, pooled libraries were again transformed into E. coli, and the extracts were pooled. A comprehensive sequencing analyses were performed to reveal the composition of the insert DNA region in libraries.