DEAD-box RNA helicase involved in the assembly of the 50S ribosomal subunit. Has an RNA-dependent ATPase activity, which is specific for 23S rRNA, and a 3' to 5' RNA helicase activity that uses the energy of ATP hydrolysis to destabilize and unwind short rRNA duplexes. Requires a single-stranded RNA loading site on the 3' side of the substrate helix. ATP + H2O = ADP + H(+) + phosphate Requires hairpin 92 of 23S rRNA for optimal activity. ATPase activity is stimulated by interaction of the N-terminal domain with RNA. Monomer. Contains an N-terminal domain that binds non-specifically to RNA and a C-terminal domain that binds specifically and tightly to hairpin 92 of 23S rRNA. Belongs to the DEAD box helicase family. DbpA subfamily. Truncated N-terminus.