CRYSTAL STRUCTURE OF VACCINIA VIRUS URACIL-DNA GLYCOSYLASE HYDROLASE, URACIL-DNA GLYCOSYLASE FOLD IN THE CORE: 3 LAYERS (A/B/A), AND PARALLEL BETA-SHEET OF 4 STRANDS IN THE ORDER 2134; NOVEL FEATURES: BETA-SHEETS AT N- AND C-TERMINUS 2OWQ