BIOLOGICAL ROLE OF DEOXYPENTOSE NUCLEIC ACIDS 447 



give serological reaction of proteins, nor (3) give qualitative protein color 

 reactions, nor (4) have the nitrogen-phosphorus ratio of a nucleoprotein.^^ 

 Evidences that not even very small amounts of biologically significant 

 protein are present in the purified agent are (5) the failure of trypsin and 

 chymotrypsin to inactivate the transforming agent, *^ and (6) the fact 

 that all of the amino acid detectable in acid hydrolysates is quantitatively 

 accounted for as glycine,^* and that (7) the rate at which this amino acid 

 appears in the hydrolysate is the same as that of the slow linear degrada- 

 tion of adenine to glycine, rather than that of the initially rapid, then 

 diminishing, hydrolysis of a protein or peptide."^ The last two findings 

 allowed the estimate that protein, if present at all, constituted not more 

 than 0.02% of the purified transforming preparation. These results do 

 not of course furnish any obstacle to the view that the transforming DNA 

 may interact with preexisting or newly formed protein material after it 

 enters a recipient cell. Furthermore, as will be indicated later, probably 

 only a small part of the DNA present is involved in transformations of 

 any one particular trait. 



The absence of protein, as just described, together with the fact that 

 the biological activity is associated with a single homogeneous boundary 

 in both the ultracentrifuge^^ and the electrophoretic cell"^° shows that 

 the isolated transforming agent is not associated with a virus particle, 

 chromosome fragment, or with cellular debris. The inactivation by crystal- 

 lized deoxyribonuclease does not result from the release of inhibitors but 

 from actual destruction of the high-molecular deoxynucleate material.*^ 



So far as is known, these conclusions apply to all of the bacterial trans- 

 forming agents to be discussed in the next section. All have been shown to be 

 inactiva,ted by purified deoxynuclease and some of them have been prepared 

 in a form relatively free of protein and ribonucleic acid. ^^'^^'^^ •''''•''^''^■"■^^ 



d. Instances of Bacterial Transformation by DNA 



Since the demonstration of the transfer of the Type III capsular charac- 

 ter in pneumococci, a number of other properties have been experimentally 



'1 M. McCarty and O. T. Avery, J. Expil. Med. 83, 97 (1946). 



" R. Austrian, Bull. Johns Hopkins Hosp. 90, 170 (1952). 



" R. Austrian, Biill. Johns Hopkins Hosp. 91, 189 (1952). 



''* A. Boivin, A. Delaunay, R. Vendrely, and Y. Lehoult, Experientia 1, 334 (1945). 



'6 H. E. Ale.xander and G. Leidy, J. Expil. Med. 93, 345 (1951). 



7« H. E. Alexander and W. Redman, J. Exptl. Med. 97, 797 (1953). 



" R. D. Hotchkiss, Cold Spring Harbor Symposia Quant. Biol. 16, 457 (1951). 



'8 R. Austrian and M. S. Colowick, Bull. Johns Hopkins Hosp. 92, 375 (1953). 



" R. D. Hotchkiss and J. Marmur, Proc. Nail. Acad. Sci. U. S. 40, 55 (1954). 



80 D. T. Klein and R. M. Klein, J. Bacteriol. 66, 220 (1953). 



" C. M. MacLeod and M. R. Krauss, /. Exptl. Med. 86, 439 (1947). 



82 H. E. Taylor, J. Exptl. Med. 89, 399 (1949). 



