A conditional expression vector for the cyanobacteria Synechocystis sp. strains PCC6803 and PCC6714 or Synechococcus sp. strains PCC7942 and PCC6301.

An expression vector, pFC1, has been constructed based on the promiscuous plasmid RSF1010, which provides autonomous replication in several cyanobacteria of the genera Synechocystis and Synechococcus [Mermet-Bouvier et al., Curr Microbiol 26:323-327]. pFC1 harbors the lambda cI857 repressor-encoding gene and pR promoter, followed by the lambda cro ribosome-binding site and ATG translation initiation codon. The latter is located within the unique NdeI restriction site (CATATG) of pFC1 and can be exposed after cleavage with this enzyme for in-frame fusion with the protein-coding sequence to be expressed. The Escherichia coli lacZ reporter gene cloned in pFC1 appeared to be highly expressed in heat-induced E. coli or cyanobacterial cells. In every case, beta-galactosidase amounted to at least 10% of soluble proteins.