Here we describe the characterization of the human glycosaminoglycan glucuronyltransferase I gene (GlcAT-I) and a related pseudogene. The GlcAT-I gene was localized to human chromosome 11q12-q13 by in situ hybridization of metaphase chromosomes. GlcAT-I spanned 7 kb of human genomic DNA and was divided into five exons. Northern blot analysis showed that GlcAT-I exhibited ubiquitous but markedly different expressions in the human tissues examined. The GlcAT-I promoter was approx. 3-fold more active in a melanoma cell line than in a hepatoma cell line, providing evidence for the differential regulation of the gene's expression. Stepwise 5' deletions of the promoter identified a strong enhancer element between -303 and -153 bp that included binding motifs for Ets, CREB (cAMP-response-element-binding protein) and STAT (signal transducers and activators of transcription). Screening of a human genomic library identified one additional distinct genomic clone containing an approx. 1.4 kb sequence region that shared an overall 95.3% nucleotide identity with exons 1-5 of GlcAT-I. However, a lack of intron sequences, as well as the presence of several nucleotide mutations, insertions and deletions that disrupted the potential GlcAT-I reading frame, suggested that the clone contained a processed pseudogene. The pseudogene was localized to chromosome 3. The human genome therefore contains two related GlcAT-I genes that are located on separate chromosomes.