Cloning, sequence analysis and expression of the cDNA encoding a sodium-dependent phosphate transporter from the...

We have isolated a full-length cDNA clone of 2.2 kb from a lambda ZapII NBL-1 (bovine renal epithelial cell) cDNA library using a portion of the rat renal sodium-dependent phosphate transporter cDNA as a probe. Expression of this cDNA clone in the COS cell line has shown it to specifically encode a sodium-dependent phosphate transporter from bovine renal epithelial cells. Sequence analysis of the clone showed a single open reading frame of 693 amino acids which has 70% similarity to the phosphate transporter of rat and human kidney [Magagnin, S., Werner, A., Markovich, D., Sorribas, V., Stange, G., Biber, J. & Murer, H. (1993) Proc. Natl Acad. Sci. USA 90, 5979-5983]. Hydropathy plots of the derived amino acid sequence show at least eight possible transmembrane regions, again in agreement with data for the rat and human transporters. The sequence contains nine putative N-glycosylation sites and nine potential sites for protein kinase C phosphorylation. Previously we have shown that the kinetics of phosphate transport into NBL-1 cells are significantly different to those for opossum kidney cells or rat kidney [Helps, C. & McGivan, J. (1991) Eur. J. Biochem. 200, 797-803]. This difference is presumably related to differences in the amino acid sequence between this protein and other cloned phosphate transporters.