Binds the 23S rRNA. Binds 1 zinc ion per subunit. Only 1 ligand appears to be Cys, the other are thought to be His and either backbone amides or solvent (PubMed:22196016). Part of the 50S ribosomal subunit. Proteolytically cleaved by protease VII to yield a peptide lacking residues 63-70. It is not clear if this is due to protein degradation or is a bona fide processing event in the strain used in PubMed:339950 and PubMed:10556732. In strains B, D10, MRE-600 and Q13 the only protein seen in PubMed:10556732 was full-length; the last 7 amino acids were sequenced only for strain MRE-600. Belongs to the bacterial ribosomal protein bL31 family. Type A subfamily.