Organization of the rat UDP-glucuronosyltransferase, UDPGTr-2, gene and characterization of its promoter.

A lambda clone containing the entire gene and flanking sequences for a form of UDP-glucuronosyltransferase (UDPGTr-2) that glucuronidates testosterone and the foreign compounds, 4-hydroxybiphenyl and chloramphenicol, has been isolated from a rat liver genomic library. Sequence analysis of this clone revealed that the UDPGTr-2 gene is approximately 12 kilobase pairs in length and consists of six exons. All introns were found to interrupt protein coding regions of the gene. Four transcriptional start sites have been identified and are located 34, 35, 38, and 39 base pairs (bp) upstream of the translation initiation site. The 5'-flanking region of the gene contains a TATA-like sequence, CATAAA, 22 bp from the first transcription start site, potential AP-1 and v-MYB binding sites, and four sequence motifs that have been found in genes that are expressed predominantly in the liver. A 323-bp fragment encompassing these elements was fused upstream in both orientations to the coding sequence of placental alkaline phosphatase to assay promoter activity. Transient transfection of various cultured cell lines with the chimeric DNA demonstrated that this fragment, in the correct orientation, was able to function as an efficient promoter in the rat hepatoma cell lines Reuber H4-II-E and McA-RH7777. It was, however, inactive in hepatoma cell lines from two other species and in cell lines derived from other tissues. These results are consistent with the physiological expression of the rat UDPGTr-2 gene and suggest that the proximal 5'-flanking region of the gene may contain information which limits its expression to the liver.