ISOLATION OF THE ANABAENA SP STRAIN PCC-7120 SIGA GENE IN A TRANSCRIPTIONAL-INTERFERENCE SELECTION

A transcriptional-interference selection was performed to identify gen es of Anabaena sp. strain PCC 7120 that encode DNA-binding proteins ab le to bind to the rbcL promoter. Unexpectedly, the selection yielded t he previously identified sigA gene, which encodes the principal sigma factor. Protein extracts from Escherichia coli containing the sigA gen e bound the rbcL promoter fragment in mobility shift assays, and compe tition experiments indicated binding to rbcL and glnA but not xisA or nifH upstream regions.