Biosynthesis and molecular cloning of sulfated glycoprotein 1 secreted by rat Sertoli cells: Sequence similarity with the 70-kilodalton precursor to sulfatide/G sub(M1) activator

Sulfated glycoprotein 1 (SGP-1) is one of the abundant proteins secreted by rat Sertoli cells. Pulse-chase labeling shows that SGP-1 is synthesized as a cotranslationally glycosylated 67-kilodalton (kDa) precursor which is posttranslationally modified to a 70-kDa form before secretion to the extracellular space. A plasmid cDNA library was constructed from immunopurified mRNA, and two overlapping clones coding for the entire protein coding sequence were isolated. The cDNas represent 27 nucleotides of 5' noncoding sequence, 1554 nucleotides of coding sequence, and 594 nucleotides of 3' noncoding sequence.