We have investigated an oxidoreductive regulatory pathway for the DNA binding activity of a pleiotropic cellular transcription factor, nuclear factor kappa B (NF kappa B), has been investigated by using NF kappa B prepared from the nucleus and the cytosol of the primary human T lymphocytes. We show that a cellular reducing catalyst thioredoxin (Trx) plays a major role in activation of the DNA binding of NF kappa B in vitro and stimulation of transcription from the NF kappa B-dependent gene expression. We demonstrate evidence suggesting that redox regulation of NF kappa B by Trx might be exerted at a step after dissociation of the inhibitory molecule I kappa B, a cytosolic-anchoring protein for NF kappa B. To examine the effect of Trx in intact cells, we performed transient assay with a chloramphenicol acetyltransferase-expressing plasmid under the control of human immunodeficiency virus (HIV) long terminal repeat and an effector plasmid expressing human Trx. The promoter activity from HIV long terminal repeat was greatly augmented by co-transfecting the Trx-expressing plasmid, whose effect was dependent on the NF kappa B-binding sites. These findings have suggested that cysteine residue(s) of NF kappa B might be involved in the DNA-recognition by NF kappa B and that the redox control mechanism mediated by Trx might have a regulatory role in the NF kappa B-mediated gene expression. These results may also provide a clue to understanding of the molecular process of AIDS pathogenesis and its possible biochemical intervention.