Involved, directly or indirectly, in the processing of chloroplast encoded mRNAs. Exhibits sequence-specific RNA binding and RNA remodeling activities, probably leading to the activation of translation of the target gene cluster psbB-psbT-psbH-petB-petD (PubMed:22451905). Blocks 5'-3' and 3'-5' exoribonucleases (e.g. polynucleotide phosphorylase (PNPase), RNase R) in vitro (PubMed:22451905). Necessary for intercistronic RNA processing of the psbH 5' untranslated region or the stabilization of 5' processed psbH RNAs. Also required for the synthesis of psbB (PubMed:11549768, PubMed:15918885, PubMed:22451905). May form homomultimers (PubMed:22451905). Part of a multi-subunit complex in the range of 60-190 and 600-800 kDa in chloroplast membranes (PubMed:15918885). Additional isoforms seem to exist. By continuous red light (Rc at 8 umol.m-2.s-1). In hcf107-2, reduced accumulation of 5'-end-processed psbH transcript, as well as psbB translation, resulting in disruption of photosystem II (PSII) and seedling lethal plants. Specific loss of processed RNAs with a 5' end 44nt upstream of the psbH start codon in the psbB-psbT-psbH-petB-petD gene cluster.