Sequence alignment of Fnr proteins from different bacteria and proposed domain structure of one subunit of Fnr based on the structure of its homolog Crp from E. coli . Conserved residues are shown in orange while residues which are only conserved in magnetospirilla are indicated in gray. In MSR-1, the first 37 amino acids that are absent in Crp contain three of the four Cys (Cys25, Cys28, Cys37, and C125 indicated by green stars) which ligate the [4Fe-4S] cluster. Gray boxes indicate DNA-binding motif. Single residue changes which are capable to activate transcription of nitrate reductase genes under aerobic conditions in E. coli are shown in red. Amb4369 is from M. magneticum strain and Magn03010404 is from M. magnetotacticum.