A locus on human chromosome 20 contains several genes expressing protease inhibitor domains with homology to whey acidic protein.

A locus containing 14 genes, encoding protein domains that have homology with whey acidic protein (WAP), has been identified in a region of 678 kb on human chromosome 20q12-13.1. Among them are genes of the known or postulated protease inhibitors elafin, secretory leucocyte protease inhibitor, human epididymis gene product 4, eppin, and huWAP2. Nucleotide sequences of full-length transcripts were obtained from cDNA fragments generated by rapid amplification of cDNA ends. Characteristic features of the genes are that the upstream promoter regions are devoid of TATA-boxes and that the coding nucleotides are divided into distinct exons for the signal peptide and for each WAP domain. In most cases, there is also a separate exon encompassing a few terminal codons and the 3' untranslated nucleotides. There are also examples of mixed type inhibitors, that encode inhibitor domains of both WAP and Kunitz types. Several of the genes appear to be expressed ubiquitously, but, in most cases, the highest transcript levels are found in epididymis followed by testis and trachea. Some of the genes also display high transcript levels in neural tissues. Potential biological roles of protein products could be in host defence against invading micro-organisms or in the regulation of endogenous proteolytic enzymes, of which those originating from the kallikrein gene locus on chromosome 19 are of particular interest.