Expression and secretion of A3-C1 polypeptide. Immunoprecipitation of 35 S-A3-C1 by MoAb CLB-CAg A IgG (30 μg/mL) was analyzed by 10% SDS-PAGE and autoradiography. The cellular and growth medium fractions were adjusted to equal volumes. Lane 1, culture medium; lane 2, cell lysate; lane 3, cell lysate without CLB-CAg A. Molecular weight standards are shown in kilodaltons (kDa) at the left.