3IHQ:
reference: Promoter recognition by a complex of Spx and the C-terminal domain of the RNA polymerase alpha subunit., Nakano MM, Lin A, Zuber CS, Newberry KJ, Brennan RG, Zuber P, PLoS One. 2010 Jan 13;5(1):e8664. PMID: 20084284

This OCA Structure page
uses Jmol, developed by the Jmol Development Team (documentation).