Changes in the Pattern of Protein Synthesis Induced by 3-indolylacetic Acid

Experiments have been performed to investigate whether indoleacetic acid changes the balance between the rates of synthesis of different kinds of proteins. Sub-apical sections of etiolated peas were incubated with (14)C- or (3)H-labeled amino acid, and combined to give dual-labeled tissue. Cell fractions were prepared by differential centrifugation, and the dual-labeled protein of each fraction analyzed by gel-filtration. When 2 x 10(-5)m indoleacetic acid was included with (14)C-labeled amino acid, but not with the (3)H-labeled amino acid, pronounced changes occurred in the pattern of incorporation of the (14)C label into protein. These changes were greatest in the proteins of the particulate fraction which included nuclear material. Although the pattern of incorporation of lysine was shown to be different from that of leucine, the changes induced by indoleacetic acid were quantitatively similar whichever amino acid was used as a precursor. Dual-labeled protein was further fractionated using column chromatography on DEAE-cellulose. The results suggested that the effect of indoleacetic acid may not be completely general, and that the pattern of synthesis of many proteins may be unaltered by indoleacetic acid. When tissue was preincubated with 10 mug/ml actinomycin D for 30 minutes, incorporation of amino acid into protein was reduced but not abolished. Actinomycin D did, however, prevent the changes in the pattern of protein synthesis which were induced by indoleacetic acid.