| Four out of five class IIa enzymes ( ProRS , ThrRS , HisRS and GlyRS , but not SerRS ) have a C terminal anticodon binding domain with an alpha / beta fold , not yet found in any other protein . ^^^ CONCLUSIONS : For the synthetases possessing the class IIa anticodon binding domain ( ProRS , ThrRS and GlyRS , with the exception of HisRS ) , the two anticodon bases 35 and 36 are sufficient to uniquely identify the cognate tRNA ( GG for proline , GU for threonine , CC for glycine ) , because these amino acids occupy full codon groups . ^^^ |