Isolation of NF-E2-related factor 2 (Nrf2), a NF-E2-like basic leucine zipper transcriptional activator that binds to the tandem NF-E2/AP1 repeat of the beta-globin locus control region.

TLDR

Hypersensitive site 2 of the beta‑globin locus control region contains a tandem AP1/NF‑E2 consensus repeat that is essential for enhancer activity and binds AP1 family proteins and the erythroid‑specific NF‑E2 factor. The study aims to characterize one clone, Nrf2, isolated from a cDNA library using this tandem repeat as a probe. Using the tandem repeat as a probe, the authors screened a lambda gt11 cDNA library from K562 cells and identified Nrf2, a 2.2‑kb transcript encoding a 66‑kDa basic leucine‑zipper protein homologous to NF‑E2. Nrf2 is ubiquitously expressed and, through its acidic activation domain, may mediate hypersensitive site 2 enhancer activity in erythroid cells, potentially stimulating beta‑globin transcription.

Abstract

Hypersensitive site 2 located in the beta-globin locus control region confers high levels of expression to the genes of the beta-globin cluster. A tandem repeat of the consensus sequence for the transcription factors AP1 and NF-E2 (activating protein 1 and nuclear factor erythroid 2, respectively) is present within hypersensitive site 2 and is absolutely required for strong enhancer activity. This sequence binds, in vitro and in vivo, to ubiquitous proteins of the AP1 family and to the recently cloned erythroid-specific transcription factor NF-E2. Using the tandem repeat as a recognition site probe to screen a lambda gt11 cDNA expression library from K562 cells, we isolated several DNA binding proteins. Here, we report the characterization of one of the clones isolated. The gene, which we named Nrf2 (NF-E2-related factor 2), is encoded within a 2.2-kb transcript and predicts a 66-kDa protein with a basic leucine zipper DNA binding domain highly homologous to that of NF-E2. Although Nrf2 is expressed ubiquitously, a role of this protein in mediating enhancer activity of hypersensitive site 2 in erythroid cells cannot be excluded. In this respect, Nrf2 contains a powerful acidic activation domain that may participate in the transcriptional stimulation of beta-globin genes.