Essential protein that is required for a late step of 50S ribosomal subunit assembly. Has GTPase activity that is stimulated by interaction with the immature 50S ribosome subunit. Binds to the 23S rRNA. Required for the association of ribosomal proteins rplP and rpmA with the large subunit (By similarity). Interacts with ctc. Interacts with the immature 50S ribosome subunit. 2 molecules of rbgA bind to one 50S subunit (By similarity). Belongs to the TRAFAC class YlqF/YawG GTPase family. MTG1 subfamily.