Comparison of the biosynthesis of wt-SCF²⁴⁸(soluble) and Sl^17H-SCF²⁴⁸ (soluble) isoforms of SCF. Stable stromal cell transfectants were starved of methionine-free medium, labeled with 0.5 mCi/mL of [³⁵S]-methionine, and chased for 0, 1, 2, and 3 hours with cold medium. Conditioned medium was collected from each cell line. Immunoprecipitation was performed using a rabbit polyclonal antibody. Synthesis of soluble (left panel) and cell-associated (right panel) fractions of SCF from stromal cells transfected with cDNAs listed on the left are shown. A 30-kD glycosylated SCF product is secreted from cells expressing the two cDNAs (left panel). In addition to small molecular mass proteins representing the unglycosylated forms of SCF, with time, a 43-kD mature cell-associated SCF product is observed in both the wt and the Sl^17H stromal cell transfectants, as seen in the right-hand panel.