MOLECULAR CDNA CLONING AND TISSUE DISTRIBUTION OF MESSENGER-RNA ENCODING A NOVEL ATP-BINDING CASSETTE (ABC) HALF-TRANSPORTER

The majority of proteins belonging to the ATP binding cassette (ABC) s uperfamily catalyzes translocation of substrates across biological mem branes. Employing a reverse transcription-PCR approach with degenerate primers, we have identified a full-length cDNA from rat hepatocytes e ncoding a novel ABC transporter termed umat (ubiquitously expressed ma mmalian ABC half-transporter). The deduced sequence of 836 amino acids comprises an N-terminal membrane anchor domain and a single conserved C-terminal nucleotide binding fold, specifying umat as an ABC half-tr ansporter. While the first 250 amino acid positions are highly diverge nt from other ABC transporters, clusters of conserved residues are evi dent along the rest of the protein. The greatest sequence similarity w as observed with the fission yeast heavy metal tolerance protein hmt1 (44.5% identity in a 626-amino-acid overlap). Umat mRNA, expressed in all tissues analyzed, was most abundant in testis. Substantial umat mR NA expression in cultured primary rat hepatocytes suggests that hepato cyte cultures should represent an adequate model for investigation of umat function and regulation. (C) 1998 Academic Press.