Abstract
Two open reading frames, alr0295 and alr2325, were found to encode the cAMP receptor proteins (CRPs) in the filamentous cyanobacterium Anabaena sp. PCC 7120, and were named ancrpA and ancrpB, respectively. Since cAMP-binding affinity of AnCrpA was higher than that of AnCrpB, cAMP signaling in Anabaena sp. PCC 7120 is thought to be mediated mainly by AnCrpA. The target genes for AnCrpA were screened using a DNA microarray. The results showed that the expression levels of genes composed of "nitrogen fixation islands" were clearly downregulated and several stress-response genes were upregulated. The results of the DNA microarray were confirmed by real-time RT-PCR. Electrophoretic mobility shift assays revealed that AnCrpA bound to several 5' upstream regions of the genes in "nitrogen fixation islands" in the presence of cAMP. At present, we are searching the recognition sequences of AnCrpA by performing an in vitro selection.
