Aquaporins in Saccharomyces

Aquaporin water channel proteins mediate the transport of water across cell membranes in numerous species. TheSaccharomyces genome data base contains an open reading frame (here designated AQY1) that encodes a protein with strong homology to aquaporins. AQY1 from laboratory and wild-type strains of Saccharomyces were expressed in Xenopus oocytes to determine the coefficients of osmotic water permeability (Pf). Oocytes injected with wild-typeAQY1 cRNAs exhibit high Pf values, whereas oocytes injected with AQY1 cRNAs from laboratory strains exhibit low Pf values and have reduced levels of Aqy1p due to two amino acid substitutions. When the AQY1 gene was deleted from a wild-type yeast and cells were cultured in vitro with cycled hypo-osmolar or hyper-osmolar stresses, theAQY1 null yeast showed significantly improved viability when compared with the parental wild-type strain. We conclude thatSaccharomyces cerevisiae contains at least one aquaporin gene, but it is not functional in laboratory strains due to apparent negative selection pressures resulting from in vitromethods.