Messenger ribonucleoprotein particles in dry wheat and rye embryos : In vitro translation and size distribution.

Extracts prepared from dry wheat (Triticum aestivum L.; var. Cama) and rye (Secale cereale L.; var. Celestijner) embryos exhibit relatively high endogenous messenger activities in an in vitro protein synthesizing system: up to 400 pmol leucine are incorporated per 50 μl reaction mixture; the messenger/ribosome ratio is estimated at about 0.03. Sucrose gradient analysis of the incubation mixture during cellfree protein synthesis shows a progressive in vitro polysome formation with the native endogenous mRNPs. The translation of these messengers, although dependent on initiation, follows linear kinetics. The native mRNP particles can be separated on sucrose gradients in 6 distinct size classes with sedimentation values varying from 25 S to 104 S. Their size is strongly reduced after deproteinization so that the naked mRNAs sediment in a range between 8 S and 35 S. The molecular weights of the proteins synthesized under direction of the native RNA particles range from 12,000 to 70,000 as estimated by polyacrylamide gel electrophoresis.