The TPaand TPbisoforms of the human thromboxane A2 receptor (TP) arise by differential splicing but are under the transcriptional control of two distinct promoters, termed Prm1 and Prm3, respectively (Coyle et al. 2002Eur J Biochem269, 4058–4073). The aim of the current study was to determine the key factors regulating TPbexpression by functionally charac-terizing Prm3, identifying the core promoter and the cis-acting elements regulating basal Prm3 activity.