FACTORS AFFECTING AMINO ACID INCORPORATION INTO PROTEINS BY ESCHERICHIA COLI RIBOSOMES

Abstract

In vitro incorporation of amino acids into protein by E. coli ribosomes inhibited by deoxyribonuclease was stimulated by addition of purified DNA, cytidine, guanos ine and uridine triphosphates. It was found that RNA synthesized in the same system depended on the integrity of DNA and the presence of all four nucleo-tides. The properties of the RNA made in vitro were studied by sedimentation through a sucrose gradient, and they were found to be similar to those of the messenger RNA observed after short pulse labeling in vivo. A preparation consisting largely of RNA isolated from bacterial extracts was found to stimulate amino-acid incorporation. The sedimentation constant of the active fraction corresponded to that of messenger RNA. In a cell-free system the incorporation of amino-acids into proteins depends on the synthesis of messenger RNA by DNA and the presence of a "reserve" of messenger RNA made in vivo and still active in the system.