A conserved DYW domain of the pentatricopeptide repeat protein possesses a novel endoribonuclease activity

Many plant pentatricopeptide repeat (PPR) proteins are known to contain a highly conserved C-terminal DYW domain whose function is unknown. Recently, the DYW domain has been proposed to play a role in RNA editing in plant organelles. To address this possibility, we prepared recombinant DYW proteins and tested their cytidine deaminase activity. However, we could not detect any activity in the assays we used. Instead, we found that the recombinant DYW domains possessed endoribonuclease activity and cleaved before adenosine residues in the RNA molecule. Some DYW-containing PPR proteins may catalyze site-specific cleavage of target RNA species.