Denatured DNA as a direct template for in vitro protein synthesis.

We recently reported' that certain preparations of DNA obtained from mammalian cells grown in cell culture were capable of markedly stimulating protein synthesis by an Escherichia coli cell-free system. It appeared that single-stranded DNA was acting directly as a template for protein synthesis. A detailed study of the requirements for this effect showed that RNA synthesis is not involved." 2 DNA from other sources was found to be essentially inactive. Clearly it would be of great interest if this effect could be generalized since it could provide a means for direct translation of the genetic code of DNA into amino acid sequences. It will be shown below that streptomycin, neomycin, and kanamycin can greatly enhance the ability of single-stranded DNA from every source tested to stimulate protein synthesis by an E. coli cell-free system. The unique properties of DNA prepared from mammalian cells grown in culture result from its exposure to one or more of these antibiotics in the growth medium.2 Materials and Methods.-Cell-free protein synthesis was measured with extracts of E. coli strain K12 as previously described.' The radioactive amino acids used were all obtained from New England Nuclear Corp. DNA was prepared from various sources by the methods of Berns and Thomas,3 and Marmur.4 The various DNA's of different base compositions5 originated from the following organisms: Staphylococcus aureus, 35 per cent GC; Bacillus subtilis, 42 per cent GC; E. coli, 50 per cent GC; Proteus morganii, 52 per cent GC; Aerobacter aerogenes, 55 per cent GC; Serratia marcescens, 58 per cent GC; Pseudomonas aeroginosa, 65 per cent GC; and various vertebrates, all 42 per cent GC. Salmon sperm DNA