442 ROLLIN D. HOTCHKISS 



borne cytochrome systems of yeast,^^ and partial disruption of bacterio- 

 phage formation,^^ but it is not clear whether such effects will prove to be 

 widespread or limited to a few species. 



One group of mutagenic agents seem to be metabolically related to the 

 nucleic acids. Such methylated purines as caffeine and theophylline are 

 effective mutagens for E. coli although not highly toxic for these organ- 

 isms.'*" The possibility that these bases might interfere with normal purine 

 incorporation seems somewhat substantiated by the finding that nucleo- 

 sides of the natural bases counteract the mutagenesis.^^ There are some 

 reasons to relate the mutagenic capacity of another agent of slight tox- 

 icity, manganous ion,''^ with its tendency to react with DNA.*^ 



It is known that X-radiation, a notable mutation-producing agent, 

 results in the production of such active intermediates as peroxides, and 

 H and OH radicals. It is therefore of interest that X-rays and some of 

 these by-products have disruptive effects upon DNA preparations. Iso- 

 lated calf thymus DNA becomes progressively less viscous (gradually 

 depolymerized) after X-irradiation^^"*^ or treatment with peroxides or OH 

 radicals.''^ -''^ There may also be chemical degradation.^" Not all forms of 

 DNA investigated have been shown to be degraded after X-irradiation, 

 possibly because the effectiveness of active radical formation is dependent 

 upon the presence of oxygen and water. Precipitated anhydrous DNA,"*^ 

 and the in situ material of thymus nuclei (citric acid treated)^' or plant 

 buds^^ were not apparently affected. On the other hand, irradiation of the 

 intact rat thymus," or of nucleated erythrocytes,^^ did lead to depolymeri- 



'^ B. Ephrussi, H. Hottinguer, and A.- M. Chimenes, Ann. inst. Pasteur 76, 351 



(1949); P. P. Slonimski and B. Ephrussi, ibid. 77, 47 (1949). 

 '^ R. I. de Mars, S. E. Luria, H. Fisher, and C. Levinthal, Ann. inst. Pasteur 84, 113 



(1953). 

 " A. Novick and L. Szilard, Proc. Natl. Acad. Sci. U. S. 36, 708 (1950). 

 " A. Novick and L. Szilard, Nature 170, 926 (1952). 

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(1951). 

 " R. B. Roberts and E. Aldous, Cold Spring Harbor Symposia Quant. Biol. 16, 229 



(1951). 

 « A. H. Sparrow and F. M. Rosenfeld, Science 104, 245 (1946). 

 " B. Taylor, J. P. Greenstein, and A. Hollaender, Arch. Biochem. 16, 19 (1948). 

 « G. C. Butler, Can. J. Research 27B, 972 (1949). 



^' G. Limperos and W. A. Mosher, Am. J. Roentgenol. Radium Therapy 63, 681 (1950) . 

 ^8 W. von B. Robertson, M. W. Ropes, and W. Bauer, Proc. Soc. Exptl. Biol. Med. 49, 



697 (1942). 

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62 M. J. Moses, R.J. Dubow, and A. H. Sparrow, /. Natl. Cancer Inst. 12, 232 (1951). 

 " M. Errera, Cold Spring Harbor Symposia Quant. Biol. 12, 60 (1947). 



