Temperature sensitivity of a class I tRNA synthetase induced by artificial breakage of polypeptide chain

Escherichia coli methionyl-tRNA synthetase consists of catalytic, anticodon-binding, and dimerization domains. The polypeptide was genetically cleaved and expressed as multiple subunits to investigate how peptide breakage affects the activity and stability of the enzyme. Mutants cleaved near conserved or functionally important sites were inactive. A few bipartite mutants were active, but they showed temperature sensitivity in their activity and stability. An additional cleavage of the active bipartites inactivated the enzyme, suggesting that at least two functional domains have to be covalently connected to retain the activity. This approach proves to be useful in determining the structural and functional organization of a protein.