This CD, composed mainly of bacterial single-domain proteins, includes the Thermus thermophilus (Tt) YbaK-like protein, a homolog of the trans-acting Escherichia coli YbaK Cys-tRNA(Pro) deacylase and the Agrobacterium tumefaciens ProX Ala-tRNA(Pro) deacylase and also the cis-acting prolyl-tRNA synthetase-editing domain (ProRS-INS). While ProX and ProRS-INS hydrolyze misacylated Ala-tRNA(Pro), the E. coli YbaK hydrolyzes misacylated Cys-tRNA(Pro). A few CD members are N-terminal, YbaK-ProX-like domains of an uncharacterized protein with a C-terminal, predicted Fe-S protein domain.