PROTEIN-SYNTHESIS IN A CELL-FREE SYSTEM FROM AN EXTREME THERMOPHILE - EFFECTS OF PREINCUBATION IN COLD ON POLYURIDYLIC ACID-DEPENDENT POLYPHENYLALANINE SYNTHESIS AT HIGH-TEMPERATURE

Preincubation of the reaction mixture in the cold enhanced Poly-U directed Poly-Phe synthesis by a cell-free extract of Thermus thermophilus HB8 at high temperature. The preincubation effect was most marked at 10-25.degree. C in the presence of 20 mM Mg2+. Preincubation at 65.degree. C failed to stimulate the incorporation. The presence of phenylalanyl-tRNA, Poly-U and ribosomes was essential for preincubation in the cold to be effective. A ternary complex of amino acyl-tRNA, Poly-U and a ribosome formed at low temperature was isolated by CPG-10 column chromatography; the isolated complex initiated Poly-Phe synthesis effectively at high temperature. The amount of the ternary complex formed depends on the preincubation time and the Mg2+ concentration. Since the amount of the complex correlated positively to the Poly-Phe synthesis rate at high temperature, the effectiveness of preincubation in the cold is presumably due to the formation of the ternary complex of phenylalanyl-tRNA, Poly-U and a ribosome.