Mutations in residues involved in zinc binding in the catalytic site of Escherichia coli threonyl-tRNA synthetase confer a dominant lethal phenotype.
Escherichia coli threonyl-tRNA synthetase is a homodimeric protein that acts as both an enzyme and a regulator of gene expression: the protein aminoacylates tRNA(Thr) isoacceptors and binds to its own mRNA, inhibiting its translation. The enzyme contains a zinc atom in its active site, which is essential for the recognition of threonine. Mutations in any of the three amino acids forming the zinc-binding site inactivate the enzyme and have a dominant negative effect on growth if the corresponding genes are placed on a multicopy plasmid. We show here that this particular property is not due to the formation of inactive heterodimers, the titration of tRNA(Thr) by an inactive enzyme, or its misaminoacylation but is, rather, due to the regulatory function of threonyl-tRNA synthetase. Overproduction of the inactive enzyme represses the expression of the wild-type chromosomal copy of the gene to an extent incompatible with bacterial growth.
Caillet
Joël
J
CNRS UPR9073, Université de Paris VII, Institut de Biologie Physico-Chimique, 13 rue Pierre et Marie Curie, 75005 Paris, France.
Graffe
Monique
M
Eyermann
Flore
F
Romby
Pascale
P
Springer
Mathias
M
D020134:Catalytic Domain / Q000235:genetics; D019281:Dimerization; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development; D015964:Gene Expression Regulation, Bacterial; D009154:Mutation; D010957:Plasmids / Q000235:genetics; D011485:Protein Binding; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013914:Threonine-tRNA Ligase / Q000235:genetics* / Q000378:metabolism; D015032:Zinc / Q000378:metabolism*
D012333:RNA, Messenger; D013914:Threonine-tRNA Ligase; D015032:Zinc