Nogalonic acid methyl ester cyclase (SnoaL) catalyzes the last ring-closure step in the biosynthesis of the polyketide antibiotic nogalamycin. Crystals of a complex of SnoaL with the substrate nogalonic acid methyl ester have been obtained using PEG 4000 as precipitant. The crystals are orthorhombic, space group I222, with unit-cell parameters a = 69.1, b = 72.0, c = 65.4 Å. They diffract to 1.35 Å resolution using synchrotron radiation. A Matthews coefficient of 2.0 Å3 Da−1 suggests one subunit in the asymmetric unit. Diffraction data for an isomorphous uranium derivative were collected and a difference Patterson map showed strong peaks which allowed determination of the position of the uranium ions.