As an approach to characterizing all human ATP-binding cassette (ABC) superfamily genes, a search of the human expressed sequence tag (EST) database was performed using sequences from known ABC genes. A total of 105 clones, containing sequences of potential ABC genes, were identified, representing 21 distinct genes. This brings the total number of characterized human ABC genes from 12 to 33. The new ABC genes were mapped by PCR on somatic cell and radiation hybrid panels and yeast artificial chromosomes (YACs). The genes are located on human chromosomes 1, 2, 3, 4, 6, 7, 10, 12, 13, 14, 16, 17 and X; at locations distinct from previously mapped members of the superfamily. The characterized genes display extensive diversity in sequence and expression pattern and this information was utilized to determine potential structural, functional and evolutionary relationships to previously characterized members of the ABC superfamily.

BACKGROUND: Multidrug resistance-associated protein (MRP) and canalicular multispecific organic anion transporter (cMOAT) are transporter proteins that pump organic anions across cellular membranes and have been linked to resistance to cytotoxic drugs. We previously identified MOAT-B, an MRP/cMOAT-related transporter, by use of a polymerase chain reaction approach. However, analysis of expressed sequence tag (EST) databases indicated that there might be additional MRP/cMOAT-related transporters. To further define the MRP/cMOAT subfamily of transporters, we used EST probes to isolate complementary DNAs for two related transporter proteins, MOAT-C and MOAT-D. METHODS: MOAT-C and MOAT-D expression patterns in human tissues were determined by RNA blot analysis, and chromosomal localization of the genes was determined by fluorescence in situ hybridization. RESULTS: MOAT-C is predicted to encode a 1437-amino-acid protein that, among eukaryotic transporters, is most closely related to MRP, cMOAT, and MOAT-B (about 36% identity). However, MOAT-C is less related to MRP and cMOAT than MRP and cMOAT are to each other (about 48% identity). Like MOAT-B, MOAT-C lacks an N-terminal membrane-spanning domain, indicating that the topology of this protein is similarly distinct from that of MRP and cMOAT. MOAT-D is predicted to encode a 1527-amino-acid protein that is the closest known relative of MRP (about 58% identity). MOAT-D is also highly related to cMOAT (about 47% identity). The presence of an N-terminal membrane-spanning domain indicates that the topology of MOAT-D is quite similar to that of MRP and cMOAT. MOAT-C transcripts are widely expressed in human tissues; however, MOAT-D transcript expression is more restricted. The MOAT-C and MOAT-D genes are located at chromosomes 3q27 and 17q21.3, respectively. CONCLUSIONS: On the basis of amino acid identity and protein topology, the MRP/cMOAT transporter subfamily falls into two groups; the first group consists of MRP, cMOAT, and MOAT-D, and the second group consists of MOAT-B and MOAT-C.

>sp|O15438|MRP3_HUMAN Canalicular multispecific organic anion transporter 2 (Multidrug resistance-associated protein 3) (ABC transporter MOAT-D) - Homo sapiens (Human).
MDALCGSGELGSKFWDSNLSVHTENPDLTPCFQNSLLAWVPCIYLWVALPCYLLYLRHHCRGYIILSHLSKLKMVLGVLL
WCVSWADLFYSFHGLVHGRAPAPVFFVTPLVVGVTMLLATLLIQYERLQGVQSSGVLIIFWFLCVVCAIVPFRSKILLAK
AEGEISDPFRFTTFYIHFALVLSALILACFREKPPFFSAKNVDPNPYPETSAGFLSRLFFWWFTKMAIYGYRHPLEEKDL
WSLKEEDRSQMVVQQLLEAWRKQEKQTARHKASAAPGKNASGEDEVLLGARPRPRKPSFLKALLATFGSSFLISACFKLI
QDLLSFINPQLLSILIRFISNPMAPSWWGFLVAGLMFLCSMMQSLILQHYYHYIFVTGVKFRTGIMGVIYRKALVITNSV
KRASTVGEIVNLMSVDAQRFMDLAPFLNLLWSAPLQIILAIYFLWQNLGPSVLAGVAFMVLLIPLNGAVAVKMRAFQVKQ
MKLKDSRIKLMSEILNGIKVLKLYAWEPSFLKQVEGIRQGELQLLRTAAYLHTTTTFTWMCSPFLVTLITLWVYVYVDPN
NVLDAEKAFVSVSLFNILRLPLNMLPQLISNLTQASVSLKRIQQFLSQEELDPQSVERKTISPGYAITIHSGTFTWAQDL
PPTLHSLDIQVPKGALVAVVGPVGCGKSSLVSALLGEMEKLEGKVHMKGSVAYVPQQAWIQNCTLQENVLFGKALNPKRY
QQTLEACALLADLEMLPGGDQTEIGEKGINLSGGQRQRVSLARAVYSDADIFLLDDPLSAVDSHVAKHIFDHVIGPEGVL
AGKTRVLVTHGISFLPQTDFIIVLADGQVSEMGPYPALLQRNGSFANFLCNYAPDEDQGHLEDSWTALEGAEDKEALLIE
DTLSNHTDLTDNDPVTYVVQKQFMRQLSALSSDGEGQGRPVPRRHLGPSEKVQVTEAKADGALTQEEKAAIGTVELSVFW
DYAKAVGLCTTLAICLLYVGQSAAAIGANVWLSAWTNDAMADSRQNNTSLRLGVYAALGILQGFLVMLAAMAMAAGGIQA
ARVLHQALLHNKIRSPQSFFDTTPSGRILNCFSKDIYVVDEVLAPVILMLLNSFFNAISTLVVIMASTPLFTVVILPLAV
LYTLVQRFYAATSRQLKRLESVSRSPIYSHFSETVTGASVIRAYNRSRDFEIISDTKVDANQRSCYPYIISNRWLSIGVE
FVGNCVVLFAALFAVIGRSSLNPGLVGLSVSYSLQVTFALNWMIRMMSDLESNIVAVERVKEYSKTETEAPWVVEGSRPP
EGWPPRGEVEFRNYSVRYRPGLDLVLRDLSLHVHGGEKVGIVGRTGAGKSSMTLCLFRILEAAKGEIRIDGLNVADIGLH
DLRSQLTIIPQDPILFSGTLRMNLDPFGSYSEEDIWWALELSHLHTFVSSQPAGLDFQCSEGGENLSVGQRQLVCLARAL
LRKSRILVLDEATAAIDLETDNLIQATIRTQFDTCTVLTIAHRLNTIMDYTRVLVLDKGVVAEFDSPANLIAARGIFYGM
ARDAGLA