ISOLATION AND CHARACTERIZATION OF A MAMMALIAN HOMOLOG OF THE DROSOPHILA WHITE GENE

The Drosophila melanogaster white gene is a member of the ABC transpor ter superfamily of ATPase transmembrane proteins and is involved in th e cellular uptake of guanine and tryptophan. We have cloned and sequen ced human and mouse homologs of white which share 55-58% amino acid si milarity with the Drosophila protein. Northern analysis reveals that t he mammalian homolog is highly expressed in several tissues, including brain, spleen, lung and placenta. We have localized the gene to human chromosome 21q22.3 by means of fluorescence in situ hybridization and linkage analysis using a (CA)(n) polymorphism. The human homolog maps to the interval between D21S212 and D21S171, a region which includes loci for bipolar affective disorder and a recessive form of deafness. Since tryptophan is a precursor for the neurotransmitter serotonin and neurotoxic metabolites of the kynurenine pathway, we propose that the human homolog of white is a suitable candidate gene for these neurolo gical disorders in humans.