Table 5.

Error correction by bacterial editing aminoacyl-tRNA synthetases^a

aaRS	Amino acids misactivatedb	Editing domainc	Pretransfer editing	Posttransfer editing	trans editing
Class I
IleRS	V, T, C	CP1	+ d	+	No
ValRS	I, T, C, S, A	CP1	+ d	+	No
LeuRS	I, M, V, D, N	CP1	+	+	No
MetRS	Only nonstandarde	Aminoacylation site	+ d	?	No
Class II
SerRS	T, C	No separate editing domain	+	–	No
ThrRS	S, V	N2 subdomain or paralog	– f	+	+
ProRS	A, C	INS insertion or paralog	+	+	+
LysRS	M, L, C, A, T	Aminoacylation site	+	–	No
AlaRS	G, S, C	C-terminal domain or paralog	+ d, g	+	+
PheRS	Y, I, L, M	B3/B4 subdomain	+	+	No

^a Data are retrieved from references 38, 248, 325, and 377.

^b Only standard amino acids are given; for amino acids in italics, the relative rate of activation is extremely low (38, 377).

^c Only mischarging with misactivated amino acids is given – note that most of the editing aaRSs also can misrecognize tRNA and catalyze mischarging with their cognate amino acid (mostly under particular conditions, either in vitro and in vivo, e.g., reference 37).

^d On the basis of increased rates of the ATP–PP_i exchange reaction.

^e Homocysteine, norleucine, ethionine, selenomethionine (activated selenomethionine is transferred to tRNA^Met and not edited, a useful property for crystallography since this allows production of selenomethionine-labeled proteins used for phasing by the Multiwavelength Anomalous Dispersion, or MAD, method [see references 378 and 379]).

^f A Zn²⁺ ion prevents misactivation of valine (isosteric with threonine) but does not prevent serine activation (see reference 380).

^g No definitive and direct structural proof.