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. One of the proteins that surrounds the polypeptide exit tunnel on the outside of the subunit. Contacts trigger factor (TF) when it is bound to the ribosome; this contact may expose a hydrophobic crevice in TF (PubMed:16271892). Part of the 50S ribosomal subunit. Contacts trigger factor when it is bound to the ribosome (PubMed:16271892). Belongs to the universal ribosomal protein uL24 family.