Human Sulfotransferases SULT1C1 and SULT1C2: cDNA Characterization, Gene Cloning, and Chromosomal Localization Robert R. Freimuth,* Rebecca B. Raftogianis,* ,1 ThomasC. Wood,* Eunpyo Moon,² , ‡ Ung-Jin Kim,² Jingping Xu,§ Michael J. Siciliano,§ and Richard M. Weinshilboum* ,2 * Department of Molecular Pharmacology and Experimental Therapeutics, Mayo Medical School/Mayo Graduate School/Mayo Clinic, Rochester, Minnesota 55905; ² Division of Biology, California Institute of Technology, Pasadena, California 91125; ‡Department of Biological Sciences, Ajou University, Suwon, Korea; and §University of Texas, M.D. Anderson Cancer Center, Houston, Texas 77030 Received October 28, 1999; accepted January 28, 2000 Sulfate conjugation catalyzed by sulfotransferase (SULT) enzymes is an important pathway in the bio- transformation of many drugs, other xenobiotics, neu- rotransmitters, and hormones. We previously de- scribed a human cDNA, SULT1C1, that encoded a protein similar in sequence to that of rat ST1C1. Sub- sequently, a related human cDNA, SULT1C2, was re- ported. In the present study, we set out to characterize further the human SULT1C1 cDNA and then to clone, structurally characterize, and map its gene. As an ini- tial step, we performed 5- and 3-RACE with SULT1C1 cDNA. Those experiments demonstrated that a small number of SULT1C1 transcripts contained an “insert,” which we later showed resulted from alternative splic- ing that involved an Alu sequence in intron 3 of SULT1C1. We then cloned and structurally character- ized the SULT1C1 gene from a human genomic BAC library. Because the sequence of SULT1C2 was closely related to that of SULT1C1 and because the genes for other human SULT paralogues occur in clusters, we screened the BAC clones that had been positive for SULT1C1 to search for SULT1C2 and discovered a clone that contained both genes. That BAC was used to sequence and structurally characterize SULT1C2. SULT1C1 and SULT1C2 were approximately 21 and 10 kb in length, respectively. Both genes contained seven exons that encoded protein, and both had structures that were similar to those of other genes that encode members of the SULT1 family. Finally, human SULT1C1 and SULT1C2 mapped to 2q11.2 by fluores- cence in situ hybridization. The cloning and structural characterization of SULT1C1 and SULT1C2 will now make it possible to perform molecular genetic and pharmacogenomic studies of these sulfate-conjugat- ing enzymes in humans. © 2000 Academic Press INTRODUCTION Sulfate conjugation is an important pathway in the biotransformation of many exogenous and endogenous compounds (Weinshilboum and Otterness, 1994; Falany, 1997). The cytosolic sulfotransferase (SULT) 3 enzymes that catalyze these reactions are members of a gene superfamily that currently includes over 35 proteins (Weinshilboum et al., 1997). In mammals, this superfamily can be divided into two families, SULT1 (phenol SULTs) and SULT2 (hydroxysteroid SULTs) (Table 1). Members of each of these families share at least 45% amino acid sequence identity, while mem- bers of subfamilies within families include proteins that share at least 60% amino acid sequence identity (Weinshilboum et al., 1997). Those subfamilies include the phenol (1A), thyroid hormone (1B), hydroxy- arylamine (1C), and estrogen (1E) SULT subfamilies (see Table 1) (Weinshilboum and Otterness, 1994; Falany, 1997; Weinshilboum et al., 1997; Her et al., 1997; Wang et al., 1998). Table 1 also shows that SULT1A1, 1A2, and 1A3 map to a gene cluster on the short arm of chromosome 16, both SULT1B1 and 1E1 map to 4q13, and the two known human hydroxy- steroid SULTs, 2A1 and 2B1, map to the long arm of chromosome 19. As described subsequently, the exis- tence of these human SULT gene clusters influenced the strategy that we used to clone the human SULT1C2 gene. The human SULT1C1 cDNA had originally been cloned from a fetal liver–spleen cDNA library (Her et Sequence data from this article have been deposited with the EMBL/GenBank Data Libraries under Accession Nos. AF186251– AF186256 (SULT1C1 cDNA), AF186257–AF186262 (SULT1C1 gene), and AF186263 (SULT1C2 gene). 1 Present address: Department of Pharmacology, Fox Chase Can- cer Center, Philadelphia, PA 19111. 2 To whom correspondence and reprint requests should be ad- dressed. Telephone: (507) 284-2246. Fax: (507) 284-9111. E-mail: weinshilboum.richard@mayo.edu. 3 Abbreviations used: 4-NP, 4-nitrophenol; BAC, bacterial artifi- cial chromosome; FISH, fluorescence in situ hybridization; ORF, open reading frame; PAPS, 3'-phosphoadenosine-5'-phosphosulfate; SULT, sulfotransferase; PCR, polymerase chain reaction; RACE, rapid amplification of cDNA ends; RAGE, rapid amplification of genomic DNA ends; UTR, untranslated region. Genomics 65, 157–165 (2000) doi:10.1006/geno.2000.6150, available online at http://www.idealibrary.com on 157 0888-7543/00 $35.00 Copyright © 2000 by Academic Press All rights of reproduction in any form reserved.