OVEREXPRESSION OF THE SODIUM ATPASE OF SACCHAROMYCES-CEREVISIAE - CONDITIONS FOR PHOSPHORYLATION FROM ATP AND P-I

The ENA1 gene of Saccharomyces cerevisiae encodes a putative ATPase ne cessary for Na+ efflux, Plasma membranes and intracellular membranes o f a yeast strain overexpressing the ENA1 gene contain significant amou nts of ENA1 protein. Consequences of the overexpression with reference to the wild-type strain are: (I) a 5-fold higher content of the ENA1- protein in plasma membranes; (2) lower Na+ and Li+ effluxes; (3) sligh tly higher Na+ tolerance; and (4) much higher Li+ tolerance. The ENA1- specific ATPase activity in plasma membrane preparations of the overex pressing strain was low, but an ENA1 phosphoprotein was clearly detect ed when the plasma membranes were exposed to ATP in the presence of Na + or to P-i in the absence of Na+. The characteristics of this phospho protein, which correspond to the acyl phosphate intermediaries of P-ty pe ATPases, the absolute requirement of Na+ or other alkali cations fo r phosphorylation, and the Na+ and pH dependence of phosphorylation fr om ATP and P-i suggest that the product of the ENA1 gene may be a Na,H -ATPase, which can also pump other alkali cations. The role of the int racellular membranes structures produced with the overexpression of EN A1 in Na+ and Li+ tolerances and the existence of a beta-subunit of th e ENA1 ATPase are discussed. (C) 1997 Elsevier Science B.V.