A SACCHAROMYCES-CEREVISIAE MUTANT LACKING A K+ H+ EXCHANGER/

The KHA1 gene corresponding to the open reading frame YJL094c (2.62 kb ) encoding a putative K+/H+ antiporter (873 amino acids) in Saccharomy ces cerevisiae was disrupted by homologous recombination, The core pro tein is similar to the putative Na+/H+ antiporters from Enterococcus h irae (NAPA gene) and Lactococcus lactis (LLUPP gene) and the putative K+/H+ exchanger from Escherichia coli (KEFC gene). Disruption of the K HA1 gene resulted in an increased K+ accumulation and net influx witho ut a significant difference in efflux, as well as an increased growth rate, smaller cells, and twice the cell yield per glucose used. Flow c ytometry analysis showed an increase of the DNA duplication rate in th e mutant. Kinetic studies of Rb-86(+) uptake showed the same saturable system for wild-type and disruptant strains. Mutant cells also produc ed a greater acidification of the medium coincident with an internal p H alkalinization and showed a higher oxygen consumption velocity. We s peculate that higher K+ accumulation and increased osmotic pressure ac celerate the cell cycle and metabolic activity.