This is the proline-rich C-terminal domain found in ribosomal protein S12 methylthiotransferase accessory factor YcaO. It has been shown to be involved in both C protein recognition and cyclodehydration. The C-terminal domain resembles a tetratricopeptide repeat that mediates dimerization [1].

1: Discovery of a new ATP-binding motif involved in peptidic azoline biosynthesis. Dunbar KL, Chekan JR, Cox CL, Burkhart BJ, Nair SK, Mitchell DA; Nat Chem Biol. 2014;10:823-829. PMID:25129028