Plays a major role in single RNA editing events in chloroplasts. Acts as a site-recognition transacting factor involved in the edition of the site 5 of ndhB1 and ndhB2 (ndhB1-5 and ndhB2-5 sites corresponding to cytidine-830), which are plastid-encoded subunits of the NADH-plastoquinone oxidoreductase. May provide the catalytic activity for editing site conversion. Binds 2 zinc ions per subunit. Belongs to the PPR family. PCMP-H subfamily.