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. It makes multiple contacts with different domains of the 23S rRNA in the assembled 50S subunit and ribosome (By similarity). The P.aeruginosa S10 leader is not regulated by the E.coli L4 protein. This and other data strongly suggest the S10 operon is regulated differently than in E.coli. Forms part of the polypeptide exit tunnel. Part of the 50S ribosomal subunit. Belongs to the universal ribosomal protein uL4 family.