This protein binds to 23S rRNA in the presence of protein L20. Part of the 50S ribosomal subunit (PubMed:387076, PubMed:10094780, PubMed:16272117, PubMed:25310980, PubMed:24844575, PubMed:27934701, PubMed:27906160, PubMed:27906161). Contacts protein L20 (PubMed:2665813, PubMed:6170935). Belongs to the bacterial ribosomal protein bL21 family.