Fig. 1. Subcellular fractionation of Fj in cultured cells. (A) Schematic diagram of the Fj protein, showing the relevant domains referred to in the text. Tm, transmembrane domain; Ag, approximate extent of the antigen used to generate anti-FjC. (B) Western blot analysis of Fj expression. Lane 1: expression of the C-terminal domain of Fj in bacterial cells. The slowest migrating band, of M_r 63.5x10³, represents the intact C-terminal domain. Considerable protein degradation occurs. The arrow indicates a fragment of approximate M_r 20x10³, used as the antigen (Ag) to generate anti-FjC. Lanes 2-7: subcellular fractionation of heat-shocked S2:fj cells containing a HS-fj cDNA insertion. S100, 100,000 g supernatant; P4, 4000 g pellet; P100, 100,000 g pellet; pellet (p) and supernatant (s) after treatment of the P100 pellet with either PBS or 0.1 M Na₂CO₃ (ALK). Lanes 8-11: expression of Fj in intact, washed cells (c) and extracellular medium (s) of S2 cells with (+) or without (-) the HS-fj cDNA (pHS-fj) insertion. The lines at the far left designate Fj-specific bands. The blot was developed with anti-FjC.