Covalently linking the Escherichia coli global anaerobic regulator FNR in tandem allows it to function as an oxygen stable dimer

► Covalently linking two alleles of FNR in tandem enhances its in situ dimerization. ► (FNRD154A)2 exhibits significantly higher binding affinities to its various DNA targets. ► (FNRD154A)2 retains transcriptional regulation activity and O2 responsive capability.