Glycyl-tRNA synthetase: an oligomeric protein containing dissimilar subunits

Glycyl-tRNA synthetase from Escherichia coli is a tetramer containing two small (33,000 daltons) and two large (80,000 daltons) subunits. The subunits can be separated and then reassembled to form active enzyme. Genetically altered glycyl-tRNA synthetases are modified in either the large or the small subunit. Wild type activity can be reconstituted in vitro by mixing extracts containing enzymes with modifications in different subunits.