One of two assembly initiator proteins, it binds directly to the 5'-end of the 23S rRNA, where it nucleates assembly of the 50S subunit. Stabilizes the tertiary rRNA structure within the 23S rRNA domain (domain I) to which it binds. Located at the polypeptide exit tunnel on the outside of the subunit. Part of the 50S ribosomal subunit. Interacts weakly with protein L4. Belongs to the universal ribosomal protein uL24 family.