NKX3.1 (Homeobox protein NK-3 homolog A) is a 32-38 kDa member of the NK-3 homeobox family of transcription factors. It is expressed in testis and prostatic epithelium, and appears to be regulated by both testosterone and estrogen (but not progesterone). NKX3.1 apparently promotes prostate gland development, and acts as a tumor suppressor/transcriptional repressor by interacting with HDAC-1 and increasing p53 acetylation and half-life. Human NKX3.1 is 234 amino acids (aa) in length. It contains a DNA binding homeodomain (aa 124-183) and phosphorylation sites at Ser185 and Ser196 that regulate protein turnover. There are four splice variants that show changes N-terminal to the homeobox domain. Deletions of aa 8-56, 13-87, 15-83 and 40-83 are all reported. Over aa 1-123, human NKX3.1 shares 50% aa identity with mouse NKX3.1.