This is a family of cysteine protease that are found to cleave the N-terminus extension of ribosomal subunit L27 in eubacteria. Proteins in this family are distinguished by a pair of invariant histidine and cysteine residues with conserved spacing that form the classic catalytic dyad of a cysteine protease [1].

1: Specific N-terminal cleavage of ribosomal protein L27 in Staphylococcus aureus and related bacteria. Wall EA, Caufield JH, Lyons CE, Manning KA, Dokland T, Christie GE; Mol Microbiol. 2014; [Epub ahead of print] PMID:25388641