Specificity of the binding of antibodies to polysomes in hen oviduct

Abstract

Experiments are presented that show the specificity of the binding of antibodies to polysomes. Polysomes engaged in the synthesis of two different proteins, conalbumin and ovalbumin, were identified by the binding of iodinated antibodies to hen oviduct polysomes. The binding sites can be saturated by preincubation of the polysomes with the specific unlabeled anti-body. Anti-conalbumin does not inhibit the binding of anti-ovalbumin and vice versa. The distribution of 125I-labeled anti-conalbumin and 131I-labeled anti-ovalbumin in the polysome profile shows that conalbumin-synthesizing polysomes are larger than polysomes involved in ovalbumin synthesis, as expected from the molecular weights of the proteins. Hen oviduct polysomal RNA can direct the synthesis of conalbumin in a cell-free system from rabbit reticulocytes. The product synthesized in vitro shows almost identical mobility with authentic [ 14C] conalbumin during electrophoresis in sodium dodecylsulfate—polyacrylamide gels. In sucrose gradients conalbumin mRNA activity is localized on the heavier side of 18 S rRNA while ovalbumin mRNA migrates more slowly, a finding that is consistent with the size of the proteins and their specific polysomes.