PORCINE ALPHA(1,3)-GALACTOSYLTRANSFERASE - TISSUE-SPECIFIC AND REGULATED EXPRESSION OF SPLICING ISOFORMS

Expression of the Gal alpha(1,3) Gal epitope on membrane glycolipids a nd glycoproteins is known to vary widely from one tissue to another. I n the course of studying the mechanisms underlying this variability, w e have isolated from pig cDNA four sequences corresponding to four iso forms of alpha(1,3)-galactosyltransferase (alpha(1,3)GT), the Golgi en zyme that links galactose in alpha(1,3) on the galactose residue of N- acetyllactosamine. The isoforms differ from each other in the alternat ive presence of two nucleotide stretches of 36 and 63 base pairs in a segment encoding the stem region of the protein. Stable expression exp eriments show that all four isoenzymes can confer alpha-galactosyltran sferase activity to HeLa cells, and that they are all located within t he Golgi compartment, indicating that variations in length in the stem region do not affect enzyme activity or cellular localization. Analys is of RNA from different pig organs and cells shows quantitative diffe rences between tissues in levels of alpha(1,3)GT, as well as qualitati ve differences, the four isoforms being unequally represented in diffe rent tissues.