Construction of Antisense RNA-mediated Gene Knock-downStrains in the Cyanobacterium sp. PCC 7120.

sp. PCC 7120 (hereafter ) is a model cyanobacterium to study nitrogen fixation, cellular differentiation and several other key biological functions that are analogous in plants. As with any other organism, many genes in encode an essential life function and hence cannot be deleted, causing a bottleneck in the elucidation of its genomic function. Antisense RNA (asRNA) mediated approach renders the study of essential genes possible by suppressing (but not completely eliminating) expression of the target gene, thus allowing them to function to some extent. Recently, we have successfully implemented this approach using the strong endogenous promoter of the gene (D1 subunit of Photosystem II) introduced into a high-copy replicative plasmid (pAM1956) to suppress the transcript level of the target gene (encoding a sigma factor, SigJ/Alr0277) in . This protocol represents an efficient and easy procedure to further explore the functional genomics, expanding the scope of basic and applied research in these ecologically important cyanobacteria.