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). This protein when expressed in E.coli represses the endogenous S10 operon; this may not occur in B.stearothermophilus however. Forms part of the polypeptide exit tunnel. Part of the 50S ribosomal subunit. Erythromycin, niddamycin, oleandomycin and spiramycin-resistant strains have changes in this protein as seen by gel electrophoresis; the nature of these changes has not been determined. Belongs to the universal ribosomal protein uL4 family.