Binds and cleaves RNA, particularly in stem-loops. Associates with pre-ribosomal particles in chloroplasts, and participates in chloroplast ribosomal RNA metabolism, probably during the final steps of 23S rRNA maturation. May enhance transcription by the plastid-encoded polymerase and translation in plastid via the stabilization of ribosome assembly intermediates. Required for chloroplast integrity. Involved in the regulation of the circadian system. Component of a complex made of CSP41A, CSP41B, ribosomes, and the plastid-encoded RNA polymerase. Interacts with CSP41B. Present in stromules. Lethal when associated with CSP41B disruption. Belongs to the NAD(P)-dependent epimerase/dehydratase family.