UGT1A4 is an enzyme of the glucuronidation pathway that transforms small lipophilic molecules, such as steroids, hormones, and drugs, into water-soluble, excretable metabolites. This enzyme has some glucuronidase activity towards amines, steroids, and sapogenins. This gene is part of a complex locus that encodes several UDP-glucuronosyltransferases. The locus includes thirteen unique alternate first exons followed by four common exons. Four of the alternate first exons are considered pseudogenes. Each of the remaining nine 5 exons may be spliced to the four common exons, resulting in nine proteins with different N-termini and identical C-termini. Each first exon encodes the substrate binding site, and is regulated by its own promoter.