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. ATP + H2O = ADP + H(+) + phosphate By growth at 3 degrees Celsius (PubMed:22564273), and 3.5% ethanol, repressed by 6% NaCl (PubMed:22820328). 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. Growth rate decreased at 37 and 25 degrees Celsius, slightly slower and to lower optical density at 3 degrees Celsius. No effect on motility at 25 or 3 degrees Celsius (PubMed:22564273). Belongs to the DEAD box helicase family. DbpA subfamily.