Table 1.

GatCAB activity with Asp-tRNA^Asn mutants^a

Base change	Region in tRNA	Relative Transamidase Activity (%)
Wild-type tRNAAsn		100.0
A9 → G9	D-stem	29.8
G10·C25 →A10·U25		98.7
C11·G24 →U11·A24		91.3
G13·C22 →U13·U22		70.9
U27·U43 →C27·G43	Anticodon stem	55.4
U36→A36	Anticodon loop	68.9
U36→C36		98.7
A37→G37		66.5
U47→Δ47	Variable loop	40.1
A49·U65→U49·G65	T-stem	< 0.5
A49·U65→C49·G65		62.8
A49·U65→G49·U65		49.9
A49·U65→U49·A65		< 0.5
G56→A56	T-loop	38.1
C5·G68→U5·A68	Acceptor stem	51.1
Wild-type tRNAAsp		< 0.5

^a[¹⁴C]Asp-tRNA (0.5 μM) was incubated with M. thermautotrophicus GatCAB (10 nM) at 37°C. The enzyme activity with each variant was expressed as relative percentage of conversion rate for wild type Asp-tRNA^Asn to Asn-tRNA^Asn.