DksA2, a zinc-independent structural analog of the transcription factor DksA

► Structure of the zinc-free DksA2 is similar to that of its zinc-finger paralog DksA. ► DksA2 binds in the RNA polymerase secondary channel. ► A disulfide bond formed by two DksA2 cysteines plays a minor role in DksA2 activity. ► Substitutions of the two cysteine residues destabilize DksA2 structure. Transcription factor DksA contains a four-Cys Zn2 +-finger motif thought to be responsible for structural integrity and the relative disposition of its domains. Pseudomonas aeruginosa encodes an additional DksA paralog (DksA2) that is expressed selectively under Zn2+ limitation. Although DksA2 does not bind Zn2+, it complements the Escherichia coli dksA deletion and has similar effects on transcription in vitro. In this study, structural and biochemical analyses reveal that DksA2 has a similar fold, domain structure and RNA polymerase binding properties to those of the E. coli DksA despite the lack of the stabilizing metal ion. Structured summary of protein interactions: RNAPandDksA2bindbybiochemical(View interaction) DksAandRNAPbindbybiochemical(View interaction) DksA2andDksA2bindbyX-ray crystallography(View interaction)