RtcR is a sigma54-dependent enhancer binding protein [1] thatactivates transcription of the rtcBA operon. The product of thertcA gene is an RNA 3'-terminal phosphate cyclase [2]. Thisdomain is found at the N terminus of the RtcR sequence. RtcR,and other sigma54-dependent activators, contain Pfam:PF00158 inthe central region of the protein sequence.