Human Phenol Sulfotransferase Gene Contains Two Alternative Promoters: Structure and Expression of the Gene

Abstract

Phenol sulfotransferases catalyze the transfer of a sulfonate moiety from 3′-phosphoadenosyl 5′-phosphosulfate to a phenolic group of lipophylic substrates to generate soluble sulfate esters. Using a phenol sulfotransferase cDNA as probe to screen a human leukocyte genomic DNA library constructed in λEMBL3, we obtained a clone containing a complete gene sequence. Comparison of the gene sequence with that of the corresponding cDNAs, namely phenol-sulfating phenol sulfotransferase (P-PST) or thermostable sulfotransferase (TS-PST), and human aryl sulfotransferase 1 and 2 (HAST1 and HAST2) indicates that the gene possesses eight short exons separated by seven introns included in approximately 5 kb. HAST2 has a different 5′ untranslated sequence, and thus is encoded by a different mRNA species. While the nucleotide sequence corresponding to the 5′ noncoding region of P-PST (TS-PST and HAST1) is included in the exon I, the 5′ untranslated sequence of HAST2 is located in the beginning of exon Ha. The remaining sequence in exon II that is identical to both P-PST and HAST2 was termed exon IIb. Exons III to VIII, which cover the coding region and the 3′ untranslated region, are almost identical in all types of PST or AST cDNAs. These results suggest that the phenol sulfotransferase gene possesses two alternate promoters that drive the expression of the two different mRNA species in a tissue-specific manner. Transfection of chloramphenicol acetyl transferase (CAT) reporter gene vectors containing the 5′-flanking sequence upstream from exon I and exon II, respectively, in transformed human embryonal kidney (293) cells indicate that both sequences possess promoter activity with higher activity for promoter 1. RNA blot analysis indicates that human phenol sulfotransferase gene is expressed in kidney, liver, lung, leukocyte, colon, small intestine, and spleen.