This is the anticodon binding domain found in some phenylalanyl tRNA synthetases. The domain has a ferredoxin fold [1,2].

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: The crystal structure of phenylalanyl-tRNA synthetase from thermus thermophilus complexed with cognate tRNAPhe. Goldgur Y, Mosyak L, Reshetnikova L, Ankilova V, Lavrik O, Khodyreva S, Safro M; Structure 1997;5:59-68. PMID:9016717