Molecular and functional study of AQY1 from Saccharomyces cerevisiae: Roleof the C-terminal domain

The yeast YPR192w gene, which encodes a protein (Aqy1p) with strong homolog y to aquaporins (AQPs), was cloned from nine S. cerevisiae strains. The osm otic water permeability coefficient (P-f) of X. laevis oocytes expressing t he gene cloned from the Sigma 1278b strain (AQY1-1) was 5.7 times higher th an the P-f of oocytes expressing the gene cloned from other strains (AQY1-2 ). Aqy1-1p, initially cloned without its C-terminus (Aqy1-1 Delta Cp), medi ated an similar to 3 times higher water permeability than the full-length p rotein. This corresponds to a 3-fold higher protein density in the oocyte p lasma membrane, as shown by freeze-fracture electron microscopy. P-f measur ements in yeast spheroplasts confirmed the presence of functional water cha nnels in Sigma 1278b and a pharmacological study indicated that this strain contains at least a second functional aquaporin. (C) 1999 Academic Press.