Purification of histone core octamers and 2.15 Å X-ray analysis of crystals in KCl/phosphate

Intact histone octamers, produced by a new method quickly and in bulk, were crystallized in KCl/phosphate, and the X-ray data were analysed to 2.15 Å, confirming a P6₅ space group. This environment preserves the high-resolution structure of the octamers and will be useful for studying them with other functionally important molecules. The octamers form into left-handed superhelices hexagonally spaced by 158.65 Å, having a pitch of 102.57 Å with six octamers per turn. A dipotassium tetraiodo mercurate derivative had good phasing power and should prove valuable in refining the structure after molecular-replacement analysis with lower resolution coordinates; the heavy atom was isomorphously placed at a unique site between the two H3-cysteine residues in the octamer.