Nuclear genome-encoded factor involved in ribosome biogenesis in chloroplasts. Binds specific group II introns in chloroplasts and facilitates their splicing. Required for normal development of chloroplasts. ATP + H2O = ADP + H(+) + phosphate The Q motif is unique to and characteristic of the DEAD box family of RNA helicases and controls ATP binding and hydrolysis. May be due to a competing acceptor splice site. Belongs to the DEAD box helicase family. DDX21/DDX50 subfamily.