A cDNA clone encoding the 70-kilodalton subunit of the tobacco (Nicotiana tabacum var Wisconsin 38) tonoplast ATPase has been isolated. The 1.656 kilobase insert contains only open reading frame that represents more than 80% of the carrot cDNA coding region. The deduced amino acid sequence has greater than 95% sequence identity with the homologous carrot sequence. A transcript of approximately 2.7 kilobase was detected on Northern blots of tobacco poly(A)(+) selected or total RNA using labeled probe produced from this clone. The gene was expressed throughout the growth cycle in unadapted and 428 millimolar NaCl adapted cells. Transcription of the 70-kilodalton subunit gene or mRNA stability was induced by short-term NaCl treatment in NaCl adapted cells or by abscisic acid treatment in both adapted and unadapted cells. Southern analysis indicated the presence of up to four genes encoding the 70-kilodalton subunit.