CIRCADIAN CLOCK PROTEIN, TRANSFERASE, KAIC, KINASE, HEXAMER, ATP-BINDING, BIOLOGICAL RHYTHMS, DNA-BINDING, MAGNESIUM, METAL-BINDING, NUCLEOTIDE-BINDING, PHOSPHOPROTEIN, REPRESSOR, SERINE/THREONINE-PROTEIN KINASE, TRANSCRIPTION, TRANSCRIPTION REGULATION 3K0A CRYSTAL STRUCTURE OF THE PHOSPHORYLATION-SITE MUTANT S431A OF THE KAIC CIRCADIAN CLOCK PROTEIN