One of the primary rRNA binding proteins, it binds directly near the 3'-end of the 23S rRNA, where it nucleates assembly of the 50S subunit. Part of the 50S ribosomal subunit. Forms a cluster with proteins L14 and L19. The mass differences between the observed and calculated masses are suggested to be due to methylation, which is known to occur in the E.coli and R.palustris orthologs. Belongs to the universal ribosomal protein uL3 family.