The gene for MMP-22 has been identified together with the gene for MMP-21 in the Cdc2L1-2 locus at the end of the short arm of human chromosome 1, 1p36.3, which is deleted frequently in a number of tumors (Gururajan et al, 1998). The gene has been renamed MMP-23B and its sequence is almost identical with that of MMP-21. The catalytic domain of MMP-22 is related most closely to MMP-11 (stromelysin-3). The protein does not contain a highly conserved cysteine residue in the proenzyme domain, shown to be involved in the autocatalytic activation of many metalloproteinases. Multiple MMP-22 mRNAs, some of which are derived by alternative splicing, are expressed in a tissue-specific manner (Gururajan et al, 1998). For other entries pertaining to metalloproteinases see also the Metalloproteinase Dictionary section of this encyclopedia.