CRYSTAL STRUCTURE OF THE D55E MUTANT OF THE HUPR RECEIVER DOMAIN 2VUH DNA-BINDING, NUCLEOTIDE-BINDING, TRANSCRIPTION REGULATION, BERYLLIUM FLUORIDE PHOSPHORYLATION MIMIC, HUPR, ACTIVATOR, CYTOPLASM, ATP-BINDING, TWO-COMPONENT REGULATORY SYSTEM, TRANSCRIPTION, PHOSPHOPROTEIN, RESPONSE REGULATOR