[A cell-free system of protein synthesis from maize seedlings]

An amino acid incorporating system has been prepared from maize seedlings, and it has been characterized with the aid of poly-U and a "mRNA enriched fraction" from the same plant material.The rate of protein synthesis decreases proportionally with the incubation period. It seems to be related to the degradation of polysomes. The optimal Mg(2+) concentration is 20 mM for the poly-U dependent protein synthesis and 10 mM for the synthesis with endogenous polysomes. The poly-U directed polyphenylalanine synthesis is increased 12-fold by addition of exogenous sRNA. Under optimal conditions poly-U causes a 40-fold increase of the phenylalanine incorporation.A "mRNA enriched fraction" was prepared from maize seedlings using proteinase K for deproteination of polysomes. The resulting RNA was further fractionated by successive precipitation with LiCl, NaCl and ethanol and characterized by polyacrylamide gel electrophoresis. The addition of 57 μg of the mRNA-enriched sample increases the incorporation of amino acid into polypeptides by a factor of approximately 2 at a Mg(2+) concentration of 5 mM, and by a factor of 1.5 at 15 mM Mg(2+). The addition of 72 μg rRNA does not stimulate the incorporation at low Mg(2+) concentration, while at 15 mM Mg(2+) a 1.3-fold increase is observed.