The cell-surface receptors for gibbon ape leukemia virus (Glvr-1; ) and rat amphotropic virus (Ram-1; ) were recently demonstrated to serve normal cellular functions as sodium-dependent phosphate transporters [3, 4]. These transporters, called PiT-1 and PiT-2, respectively, are approximately 59% identical in amino acid sequence and are members of a gene family distinct from the renal type I and type II NaP(i) sodium-dependent phosphate transporters. Both PiT-1 and PiT-2 are widely distributed in many tissues including kidney, brain, heart, liver, muscle, and bone marrow. Expression of both transporters is increased by phosphate deprivation. The distinct structural and functional properties of these molecules establishes them as members of a new family of phosphate transporters which may play a major role in phosphate uptake in a wide variety of cell types.
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