OxyR is involved in the expression of thioredoxin reductase TrxB in Pseudomonas putida.

OxyR regulates the expression of a peroxiredoxin (AhpC) and two catalases (KatA and KatB), which play roles in peroxide protection, at the transcription level in Pseudomonas putida KT2442. Proteome analysis indicated significantly increased amounts of the enzymes AhpC, KatA, KatB, and a peroxiredoxin reductase (AhpF) in the oxyR1 mutant cells; these increases reflected the upregulation of the expression of the genes encoding these enzymes. Additionally, although the effect of oxyR1 mutation on the trxB transcript level was not clearly evident, it increased the amount of thioredoxin reductase (TrxB) by fivefold. Primer extension analysis revealed that trxB was constitutively transcribed from the P1 site; however, hydrogen peroxide treatment lowered the transcription of trxB from P1 but induced its transcription from P2. Adjacent to the -35 base of the P2 initiation site, sequences similar to those involved in the proposed OxyR binding in Escherichia coli were found in a region to which OxyR was shown to bind. These observations suggest that in P. putida, OxyR regulates TrxB expression by promoting trxB transcription from the P2 site when oxidative stresses lowered the transcription from the constitutive P1 site.