SNQ1 gene function is required for the expression of resistance to 4NQO in wild-type yeast. The sequence of a 3.7 kb yeast DNA containing the gene SNQ1 was determined. The SNQ1 gene consists of an open reading frame of 1641 bp and encodes, according to the hydrophobicity analysis of the putative protein, a transmembrane protein of 547 amino acids. Homology searches in yeast genome databanks revealed a 100% sequence homology with gene ATR1 which controls resistance to aminotriazole in S. cerevisiae. Pre-treatment of wild-type yeast, but not of snq1-0::LEU2 disruption mutants, with sublethal doses of aminotriazole induced hyper-resistance to 4-nitroquinoline-N-oxide. Partial deletion of the nucleotide sequence coding for a putative ATP-binding site has no, or little, influence on resistance to 4NQO whereas total deletion of the region coding for this ATP-binding domain leads to 4NQO-sensitive null-mutants.