The Saccharomyces cerevisiae END1 gene is required for formation or maintenance of the vacuole, for growth on non-fermentable carbon sources, for efficient mating and for growth at 37 degrees C. The END1 gene was cloned by complementation of the end1 mutation. Two end1 null mutants, constructed by disruption and deletion of the END1 gene, show features identical to the original end1 mutant. However, in this paper we correct a previous finding from our group that end1 is defective in internalization of the yeast pheromone alpha-factor. End1 mutants take up alpha-factor at the same rate as corresponding wild-type cells but the internalized pheromone is not degraded. Since whole cell respiration and respiratory control of end1 mitochondria are not impaired, it seems plausible that a defect in gluconeogenesis could partially account for the inability of end1 to grow on non-fermentable carbon sources. DNA sequence analysis of the END1 gene reveals a 3090-bp open reading frame capable of encoding a hydrophilic protein of 118 kd. The molecular mass of End1p was confirmed by immunoprecipitation. The predicted End1p sequence shows no significant similarity to other known protein sequences except for a short region of homology with the putative adenine nucleotide binding sites shared by a group of enzymes, notably ATPases.