EXPRESSION CLONING OF RAT RENAL NA+ SO4 COTRANSPORT/

Injection of rat kidney cortex mRNA into Xenopus laevis oocytes leads to a stimulation of Na+-dependent SO42- uptake. Based on this informat ion, we have isolated from a corresponding library a cDNA (NaSi-1) tha t is most likely related to a Na+/SO42- cotransport system. NaSi-1 cRN A leads in a time- and dose-dependent manner to specific stimulation o f Na+-dependent SO42- uptake in oocytes. The apparent affinity constan ts of the NaSi-1 cRNA-expressed transport resemble those of Na+/SO42- cotransport in brush-border membrane. The NaSi-1 cDNA contains 2239 bp [including a poly(A) tail] and encodes a protein of 595 amino acids ( 66.05 kDa); the hydropathy profile suggests at least eight membrane-sp anning regions. In vitro translation of NaSi-1 cRNA results in a prote in of the expected size and suggests glycosylation. Northern blot anal ysis shows signals of 2.3 and 2.9 kb in kidney (more abundant in corte x than in papilla/medulla) and in mucosa of small intestine of rats. T he above data indicate that we have structurally identified a membrane protein involved in renal and small-intestinal brush-border membrane Na+/SO42-cotransport.