title: Dispensable pieces of an aminoacyl tRNA synthetase which activate the catalytic site.
abstract: Recent data suggest that size polymorphism of aminoacyl tRNA synthetase is due to variable fusions of additional functional domains to a catalytic core so that, in a large synthetase, a substantial part of the polypeptide is dispensable for catalytic activity. We demonstrate here that a dispensable domain, joined to the catalytic core of a large synthetase, can activate the catalytic sites. This is shown by complementation of an activity-deficient mutant enzyme by protein fragments that contain internal deletions within the catalytic domain and are themselves devoid of activity. The complementation is dependent upon the presence of a defined segment of polypeptide that is remote in the sequence from the catalytic core. Substantial coupling has been established between dispensable and indispensable component pieces. This could be a mechanism to build efficiently large enzymes which integrate the catalytic sites with other previously shown functional roles.
mesh_terms: D000412:Alanine-tRNA Ligase / Q000235:genetics* / Q000378:metabolism; D000604:Amino Acyl-tRNA Synthetases / Q000235:genetics*; D001665:Binding Sites; D002872:Chromosome Deletion; D000939:Epitopes / Q000032:analysis; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005816:Genetic Complementation Test; D007074:Immunoglobulin G; D010957:Plasmids
chemical_list: D000939:Epitopes; D007074:Immunoglobulin G; D000604:Amino Acyl-tRNA Synthetases; D000412:Alanine-tRNA Ligase