LexA, a transcription regulator binding in the promoter region of the bidirectional hydrogenase in the cyanobacterium Synechocystis sp PCC 6803

The unicellular cyanobacterium Synechocystis PCC 6803 contains a single pentameric bidirectional hydrogenase encoded by hox-EFUYH. Transcriptional experiments demonstrated that the five hox genes are part of a single transcript together with three ORFs with unknown functions. The transcription start point was localized by 5' RACE to 168bp upstream the hoxE ATG start codon. DNA affinity assays demonstrated a specific interaction between the hox regulatory promoter region and a protein which, using mass spectrometry, was identified to be LexA. Overexpressed His-tagged Synechocystis LexA and EMSA showed a specific binding to the promoter region of the hox operon. Increasing concentrations of the purified LexA resulted in two retarded LexA-DNA complexes, in agreement with the presence of two putative LexA binding sites upstream the determined TSP. (c) 2005 Federation of European Microbiological Societies. Published by Elsevier B.V. All rights reserved.