Structure of the human Bach2 POZ domain. (a) Ribbon representation of the form I (Cys20 reduced) and form II (Cys20 oxidized) structures of the human Bach2 POZ domain. Secondary-structure elements of the A subunit are labelled; a prime (′) indicates a secondary-structure element of the B chain. The lower images depict an enlargement of the region surrounding the Cys20 residue; S atoms are coloured orange. A 2Fo − Fc electron-density map is shown contoured at 1.5σ. The charged pocket and lateral grooves are indicated; these regions have previously been described in other POZ-domain proteins (Ahmad et al., 1998, 2003). (b) Size-exclusion chromatograpy of wild-type and mutant Bach2 POZ domains using Superdex 75. The top left trace represents the elution profile of marker proteins (low-molecular-weight gel-filtration calibration kit; GE Healthcare). Sizes are indicated in kDa. The wild-type and mutant Bach2 POZ domains eluted at volumes corresponding to dimeric species.