Identification of a furA cis Antisense RNA in the Cyanobacterium Anabaena sp. PCC 7120

Ferric uptake regulation (Fur) proteins are prokaryotic transcriptional regulators that integrate iron metabolism with several environmental stress responses. The regulatory network that governs Fur proteins is rather complex. Control at several stages from gene transcription to post-translational binding of different ligands has been reported in Fur from Escherichia coli. In the nitrogen-fixing cyanobacterium Anabaena sp. strain PCC 7120 FurA is the product of open reading frame all1691 that is located between sigC and alr1690, the latter encoding a putative cell wall-binding protein. Anabaena FurA is an autoregulated protein whose expression increases slightly under iron deprivation. Northern blot analysis of furA expression showed an unexpected transcription pattern that consisted of two transcripts. The short transcript corresponded to furA mRNA, whereas the longer transcript contained the alr1690 mRNA and a large region that overlapped the complete furA gene and was complementary to the furA mRNA. Increased expression of FurA in a mutant unable to produce the longer message showed that this transcript acted as an antisense RNA (α-furA RNA) interfering with furA transcript translation thus contributing to determine cellular levels of FurA protein.