The KHA1 gene corresponding to the open reading frame YJL094c (2.62 kb) encoding a putative K+/H+ antiporter (873 amino acids) in Saccharomyces cerevisiae was disrupted by homologous recombination. The core protein is similar to the putative Na+/H+ antiporters from Enterococcus hirae (NAPA gene) and Lactococcus lactis (LLUPP gene) and the putative K+/H+ exchanger from Escherichia coli (KEFC gene). Disruption of the KHA1 gene resulted in an increased K+ accumulation and net influx without a significant difference in efflux, as well as an increased growth rate, smaller cells, and twice the cell yield per glucose used. Flow cytometry analysis showed an increase of the DNA duplication rate in the mutant. Kinetic studies of 86Rb+ uptake showed the same saturable system for wild-type and disruptant strains. Mutant cells also produced a greater acidification of the medium coincident with an internal pH alkalinization and showed a higher oxygen consumption velocity. We speculate that higher K+ accumulation and increased osmotic pressure accelerate the cell cycle and metabolic activity.