Nucleic Acids and Amino Acid Incorporation 179 



factors") are found in fractions which, from their physico- 

 chemical properties, are not nucleotides. It may be that 

 specific polynucleotides are activated by substances related to 

 the "incorporation factors" but definite information on this 

 point awaits the characterization of the latter factors. 

 Effect of X -irradiation on the nucleic acid response. Table I 

 shows that exposure to 150,000 r has no significant effect 



Table I 



Restoration of Glycine Incorporation by Staphylococcal Nucleic 

 Acids Before and after X-irradiation 



Increase in glycine incorporation {c.p.m.jmg.) 



Incorporation in absence of added nucleic acid =218 



on the ability of staphylococcal RNA or DNA to promote 

 glycine incorporation. These results provide a further indica- 

 tion that the ability to promote incorporation under con- 

 dition 1 resides in portions of the nucleic acid structure rather 

 than in the complete polynucleotide. 



Inhibitors 



Antibiotics. Chloramphenicol inhibits the incorporation of all 

 amino acids so far tested ; in no case does the inhibition reach 

 completion. In all cases investigated, inhibition increases with 

 increasing concentration of antibiotic but reaches a plateau 

 value which varies with the amino acid whose incorporation 

 is studied (see Table II). The synthesis of protein, whether 

 measured by increase in protein-N, catalase or ^-galactosidase, 



