Figure 1. Immunoprecipitation of membrane-bound polysomes (microsomes) with anti-Hsp47, anti-Sec61a, and anti-collagen IV antibodies after retinoic acid treatment of F9 cells. Cells treated (lanes 2, 4 and 6) or not (lanes 1, 3 and 5) with retinoic acid for 4 days were labeled for 1 h with 35S-methionine. Microsomes were immonoprecipitated with anti-Hsp47 (lanes 1 and 2), anti-Sec61a (lanes 3 and 4), and anti-collagen IV (lanes 5 and 6) antibodies. Ab: antibody; RA: all-trans retinoic acid. Molecular masses of standard proteins are given on the right side of the figure.