Protein synthesis by poly somes isolated from wheat leaves

摘要

When polysomes isolated from wheat (Triticum vulgareL., var. W2691) leaves are incubated with the soluble components of wheat germ protein synthesizing system (SI76 fraction), the in vivo initiated polypeptide chains are elongated and various size classes of polypeptides are radiolabelled. Under these conditions, there is little or no reinitiation of polypeptides by ribosomes that have completed the elongation of in vivo initiated chains. The time course of labelling and the large size of the polypeptides synthesized suggest that most of the polypeptides are elongated to completion in the cell-free system. The size classes of newly synthesized polypeptides thus reflect the size classes of wheat leaf polysomal mRNA populations.In the protein synthesizing system reconstituted with wheat leaf polysomes and S176 fraction from wheat germ, cydoheximide inhibits the elongation of certain size classes of polypeptides. At high concentrations (5×10−3M and greater), it completely abolishes the translation of all size classes of polysomal mRNA. Chloramphenicol, on the other hand, preferentially inhibits the synthesis of certain classes of polypeptides including those that correspond in size to polypeptides known to be synthesized by isolated chloroplasts.These characteristics of cell-free translation suggest that analytical gel electrophoresis of the products of polysomal mRNA translation represents a potentially powerful biochemical tool for monitoring mRNA populations in plant tissu