5.4.99.24 a proteolytically derived fragment of the enzyme consisting of residues 89-319 retains catalytic activity. Crystals of this fragment, grown by precipitation with sodium acetate at pH 8.0, belong to space group P321, with unit-cell dimensions a = b = 97.1, c = 86.3 A and have two molecules in the crystallographic asymmetric unit. Crystals diffract X-rays to at least 2.3 A resolution and appear suitable for crystal structure determination 5.4.99.24 crystals of the catalytic domain RluC(92-319) are grown at 20°C using the hanging drop method