This domain is found in histidyl, glycyl, threonyl and prolyl tRNA synthetases [1] it is probably the anticodon binding domain [2].

1: Evolution of aminoacyl-tRNA synthetases--analysis of unique domain architectures and phylogenetic trees reveals a complex history of horizontal gene transfer events. Wolf YI, Aravind L, Grishin NV, Koonin EV; Genome Res 1999;9:689-710. PMID:10447505

2: Crystal structure analysis of the activation of histidine by Thermus thermophilus histidyl-tRNA synthetase. Aberg A, Yaremchuk A, Tukalo M, Rasmussen B, Cusack S; Biochemistry 1997;36:3084-3094. PMID:9115984