TCDD-responsive region within the 5'-flanking region of the TH gene. A deletion construct containing the 5'-flanking region of the murine TH gene fused to luciferase gene was generated. On the left is a schematic representation of the deletion constructs. Numbers on each construct indicate distance in bp from a putative transcription start site of the TH gene (+1). These constructs were transiently cotransfected into Neuro2a cells with an AhR expression vector (pcDNA4-rAhR) and a β-galactosidase expression vector (pcDNA4/V5-His/LacZ). The luciferase assay was performed 24 h after exposure to 10 nM TCDD. Relative luciferase activities were normalized with β-galactosidase activities. The 5'-flanking regions of the TH gene shorter than -167 bp did not increase luciferase activity in TCDD-exposed Neuro2a cells. Data are presented as mean ± SD of three replicate determinations.