A covalent adduct between the uracil ring and the active site of an aminoacyl tRNA synthetase.

A covalent adduct of an aminoacyl tRNA synthetase and uracil nucleoside has been isolated. The enzyme adduct is catalytically inactive; one nucleoside is bound per catalytic site. The release of uridine restores enzyme activity. The nucleoside attaches to a protein segment required for tRNA interaction. The findings add support to concepts of a covalent component for some protein-nucleic acid complexes.