Human HtrA2 (also designated Omi) is a novel member of the HtrA serine protease family and is highly homologous to HtrA (also known as L56 and HtrA1). HtrA2 is ubiquitously expressed nuclear protease that is capable of autoproteolysis. The HtrA2 protein exists as two polypeptides of 38 and 40 kDa and as an alternatively spliced form called D-Omi, which is predominately expressed in the kidney, colon and thyroid. Like HtrA, HtrA2 is involved in the degradation aberrantly folded proteins during conditions of cellular stress, sμggesting that it may possess a chaperone-like role under normal conditions.