One of the primary rRNA binding proteins, this protein initially binds near the 5'-end of the 23S rRNA. It is important during the early stages of 50S assembly (By similarity). Makes multiple contacts with different domains of the 23S rRNA in the assembled 50S subunit. Forms part of the polypeptide exit tunnel, in which it helps forms a bend with protein L22. Contacts the macrolide antibiotic spiramycin in the polypeptide exit tunnel. Part of the 50S ribosomal subunit. Interacts weakly with proteins L18e, L24 and L37e. Has been cross-linked to L18e. Belongs to the universal ribosomal protein uL4 family.