278 NUCLEIC ACIDS AND GROWTH 3 



the protein metabolism of Staphylococci disrupted by ultrasonics. They found that 

 the disrupted cells are still capable of amino-acid incorporation into proteins, 

 and even of net protein synthesis, provided that energy sources (adenosinetriphos- 

 phate (ATP) and hexosediphosphate) and an adequate mixture of amino acids 

 are present. Removal of the nucleic acids by various treatments, including 

 digestion with specific nucleases, greatly inhibits protein synthesis ; addition of a 

 mixture of DNA and RNA from Staphylococci restores the activity of the system. 

 Treatment with either ribonuclease or deoxyribonuclease inactivates these 

 nucleic-acid preparations; nucleic acids from other sources are inactive. These 

 findings suggest, of course, that specific nucleic acids are needed to promote incor- 

 poration of amino acids into proteins : however, breakdown products of the spe- 

 cific staphylococcal nucleic acids, after they have been digested with nucleases, 

 are also active. The experiments further show that incorporation of amino acids 

 into proteins is different from true protein synthesis, although both processes have 

 some features in common. 



As already mentioned, Gale and Folkes (1954, 1955a) found that a mixture of 

 pyrimidines and purines stimulates adaptive synthesis of glucozymase in their 

 system, provided that amino acids are present. When the disrupted cells are 

 depleted of their nucleic acids, addition of nucleic acids stimulates the induced 

 enzyme synthesis; RNA is much more effective for catalase than DNA, while a 

 mixture of purines and pyrimidines promotes best the ^-galactosidase synthesis. 



The results can be accounted for, according to Gale and Folkes (1954, 1955a), 

 by the following hypothesis : DNA, perhaps associated with a protein, is the initial 

 organizing structure; it is incapable of synthesizing proteins itself, but it acts as an 

 organizer for the synthesis of RNA ; once RNA has been synthesized, protein synthe- 

 sis can take place at a rate dependent upon the amount of specific RNA present. 



Gale and Folkes' (1954, 1955a) results on the incorporation of amino acids into 

 proteins have been quickly confirmed by Lester (1953) and by Beljansky (1954); 

 they worked on bacteria lysed with lysozyme (so called protoplasts) and after- 

 wards treated with nucleases. 



Similar results have also been obtained with extracts from animal cells : Allfrey, 

 Daly and Mirsky (1953), and Zamecnik and Keller (1954) have found that 

 treatment with ribonuclease strongly inhibits the incorporation of labelled amino 

 acids into the proteins of the microsomes present in liver homogenates. Inci- 

 dentally, it is worth mentioning that these small cytoplasmic particles, which are 

 very rich in RNA, incorporate amino acids into their proteins in vivo and in vitro 

 much more rapidly than any other cell fraction, including mitochondria and 

 nuclei (Hultin, 1951; Siekevitz, 1952; etc.). 



Recently, Gale and Folkes (1955b) and Gale (1955) have reported on ex- 

 tremely interesting developments of their work on disrupted Staphylococci. While, 

 as mentioned earlier, non specific RNA's isolated from yeast or liver are unable 

 to restore incorporation of amino acids into the proteins, ribonuclease digests of 

 these nucleic acids are active. This observation led Gale and Folkes (1955b) to an 

 extensive fractionation of digests of staphylococcal RNA by chromatography and 

 ionophoresis : single fractions could be obtained from the digest, which promoted 

 the incorporation instead of RNA, the active fraction being different for each 



