388 RICHARD SCHWEET AND JOHN BISHOP 



ration was observed. This stimulation required addition of all four 

 nucleoside triphosphates. RNA with the sedimentation properties of 

 messenger RNA was shown to be synthesized. In addition, these authors 

 isolated an RXA fraction, by washing ribosomes in dilute magnesium 

 chloride, which also stimulated amino acid incorporation. This fraction 

 also had the sedimentation characteristics of messenger RNA. These 

 results then suggest that amino acid incorjioration depends on the DNA- 

 directed synthesis of messenger RNA and also that a reserve of the 

 latter is present in the cell-free system. 



Wood and Berg (1962) removed nucleic acids from an E. coli extract 

 by ammonium sulfate and protamine fractionation. Partially purified 

 soluble enzymes and ribosomes, when incubated with the usual com- 

 ponents, including added soluble RNA, showed low amino acid incorpo- 

 ration. DNase inhibited only slightly, and the incorporation appeared 

 similar to the residual incorporation found by others to occur in the 

 presence of DNase, e.g., due to endogenous messenger RNA. T2 phage 

 DNA and purified RNA polymerase added to the system gave a 20-fold 

 increase in incorporation. That the DNA effect was due to synthesis of 

 RNA was shown by a number of experiments. These involved two- 

 stage experiments. In the first stage, RNA synthesis was allowed to 

 proceed, or prevented, for example, by omission of UTP. This reaction 

 was stopped and then protein synthesis measured using the previous 

 reaction mixture as the stimulating component. The results showed that 

 RNA synthesized under the influence of DNA was responsible for in- 

 creased amino acifl incorporation, although more striking increases were 

 found when RNA was continuously generated in the amino acid- 

 incorporating system. Since present evidence indicates that RNA poly- 

 merase synthesized messenger RNA, it is likely that it is this type of 

 RNA which is effective. However, as in other studies in this field, final 

 proof of this hypothesis will require the demonstration that known, 

 specific proteins are synthesized under the influence of a specific DNA 

 or RNA. Such experiments appear feasible and are in progress in several 

 laboratories. An interesting aspect of these studies was the finding that 

 phage DNA was 5 times more active in stimulating incorporation than 

 E. coli DNA, and that heated phage DNA and single-stranded (^X174 

 phage DNA were inactive. These latter DNA's are efficient primers for 

 the RNA polymerase, and unless the RNA remained bound and unavail- 

 able to the protein-synthesizing system, it is difficult to understand the 

 lack of stimulation. The general concept of the role of DNA as primer 

 in the RNA polymerase reaction is that each strand of DNA produces 

 a complementary strand of RNA, resulting in production of RNA of 

 the same over-all composition as the DNA primer. With single-strand 



