Mapping and sequencing of two yeast genes belonging to the ATP-binding cassette superfamily.

ATP-binding cassette (ABC) transporters share significant sequence identity within their ATP-binding domains. Degenerate oligonucleotides based on highly conserved portions of the ATP-binding domain genes were used to clone portions of two members of the ABC gene superfamily from Saccharomyces cerevisiae DNA. These genes were designated MDL1 and MDL2 (for multidrug resistance-like). Each MDL gene is predicted to encode a single set of transmembrane domains and a single ATP-binding domain, thus the MDL gene products are 'half-molecule' ABC proteins. The two genes were mapped to precise regions on chromosomes XII and XVI and show a considerable similarity to the mammalian P-glycoprotein/multidrug resistance (MDR) and peptide transporter (TAP) genes. Preliminary analysis of null mutants constructed by gene replacement has indicated that the MDL genes are not essential for viability of yeast. The sequences have been deposited in the GenBank data library under Accession Numbers L16958 (Locus YSCBCSA) and L16959 (Locus YSCBCSB).