Subsequently, the addition of 5mM DTT to the H2O2 treated sample restored Ma P msvR binding (Figure 5, lane OR). Together, the data presented herein suggest a mechanism by which MaMsvR may act as a redox-sensitive transcription repressor at its own promoter. In the reduced state, MaMsvR binds to and likely represses LEE011 cost transcription from P msvR . Upon changes in redox conditions, MaMsvR undergoes a conformational change, rendering it unable to bind to the MsvR binding boxes [35]. Evidence presented

herein suggest that the C206 residue of MaMsvR likely contributes to this conformational change. Figure 5 Proposed Mechanism for Redox-Sensitive Transcriptional Regulation by MaMsvR. EMSA experiment with pre-reduced MaMsvR and various treatments. The P msvR DNA (10 nM) only control reaction is represented by (-). All other lanes contain P msvR DNA (10 nM)

and 200 nM MaMsvRPre-Red either in the absence (+, O) or presence (R, OR) of 5 mM DTT. Lanes labeled with (O) also contain 10 μM H2O2. Conclusions MaMsvR is a homologue of the previously characterized MthMsvR, and both proteins bind a characteristic TTCGN7-9CGAA motif that is present in the promoter regions of all MsvR homologues. In solution, MaMsvR is a dimer under non-AZD1080 reducing and reducing conditions. Both MaMsvR and MthMsvR exhibit differential DNA binding under non-reducing and reducing conditions. However, redox status has a far more obvious impact Apoptosis inhibitor on MaMsvR, which binds DNA only under reducing conditions. Modification of cysteine residues in the V4R domain in an oxidizing environment likely results in conformational changes that interfere with MaMsvR binding to the Ma P msvR DNA. Thus, derepression permits transcription under non-reducing conditions. There is an MsvR protein encoded in twenty-three of the forty fully sequenced genomes of methanogens, supporting an important, but poorly understood, role in methanogen biology. The results described here provide insight into the function and

mechanism of MaMsvR, setting the stage for future investigation of MaMsvR regulated promoters using the M. acetivorans genetic system. Methods Reagents T4 DNA ligase and Phusion™ DNA polymerase were purchased from 3-oxoacyl-(acyl-carrier-protein) reductase New England Biolabs. Fast Digest ® restriction enzymes were purchased from Fermentas. General chemicals were purchased from Fisher Scientific. Sequence analysis The M. acetivorans genome sequence (Accession number NC_003552) was downloaded into the Geneious software package [36]. All sequence manipulations were performed in Geneious and primers were designed using Primer 3 [37]. All DNA templates were confirmed by sequencing at the Oklahoma Medical Research Foundation. Transcription start site mapping The transcription start site of Ma msvR was mapped using a 5′/3′ RACE kit (Roche Applied Science). All reactions were performed according to the manufacturers’ directions.