146 Arthur L. Koch 



28), working with plants, has suggested such a mechanism to explain chromo- 

 some breakage induced with caffeine derivatives. He proposes that ATP is 

 necessary for the aberrations produced by the compound 8-ethoxy caffeine. 

 However, there appear to be considerable differences between the two systems; 

 with the bacteria one thinks the process involved is one of 'point mutation', but 

 certain clearcut differences are evident in the two types of material with regard to 

 the interaction ofoxygen tension and ionizing radiations. (Compare (2) and (27), 



4. The mutagen causes the organism to 'adapt' to its presence, and thus causes 

 widespread alterations in the amount of enzymes and intermediates. This could 

 lead to a change in mutation rate. This may be in fact the explanation of the 

 effect of adenine (12). This substance inhibits the growth of bacteria which 

 have previously been grown in its absence. Growth resumes when the organism 

 has 'adaptively' produced an 'adenine deaminase' activity which is not de- 

 monstrable in bacteria grown in its absence. This shift in metabolism can then 

 be envisioned to lead to changes in the mutation rate. 



This list is probably sufficiently inclusive to include the right answer if there 

 is only one, but at least the necessary research, both with test tubes and with 

 pencil and paper, to test these possibilities is feasible. 



REFERENCES 



1. A. NoviCK and L. Szilard: Experiments on spontaneous and chemically induced 

 mutations of bacteria growing in the chemostat. Cold Spr. Harb. Symp. Quant. Biol. 

 16, 337-343 (1951). 



2. A. Novick: Mutagens and anti-mutagens. Brookhaven Symp. Biol. No. 8, 201-214 

 (1956). 



3. A. L. Koch: The metabolism of methyl purines by Escherichia coli. I. Tracer studies. 

 J. Biol. Chem. 219, 181-188 (1956). 



4. A. L. Koch, F. W. Putnam, and E. A. Evans Jr.: The purine metabolism of Escherichia 

 coli. J. Biol. Chem. 197, 105-112 (1952). 



5. A. L. Koch: Biochemical studies of virus reproduction. XI. Acid soluble purine meta- 

 bolism. /. Biol. Chem. 203, 227-37 (1953). 



6. M. E. Balis, C. T. Lark, and D. Luzzati: Nucleotide utilization by Escherichia coli. 

 J. Biol. Chem. 212, 641-645 (1955). 



7. E. Bolton: Biosynthesis of nucleic acid in E. coli. Proc. Nat. Acad. Sci., Wash. 40, 

 764^772 (1954). 



8. A. L. Koch: The kinetics of glycine incorporation by Escherichia coli. J. Biol. Chem. 

 217, 931-945 (1955). 



9. I. A. Rose and B. S. Schweigert: Incorporation of C^* totally labeled nucleosides 

 into nucleic acids. /. Biol. Chem. 202, 635-644 (1953). 



10. E. Volkin and L. Astrachan: Phosphorus incorporation in Escherichia coli ribonucleic 

 acid after infection with bacteriophage T2. Virology 2, 149-161 (1956). 



11. J. O. Lampen: Symposium on Piwsphorus Metabolism, vol. II, ed. by W. D. McElroy and 

 B. Glass, Johns Hopkins Press, Baltimore, 363-380 (1952). 



12. A. L. Koch and W. A. Lamont: The metabohsm of methyl purines by Escherichia 

 coli. II. Enzymatic studies. /. Biol. Cliem. 219, 189-201 (1956). 



13. A. L. Koch: Some enzymes of nucleoside metabolism oi Escherichia coli. J. Biol. Cfiem. 

 223, 535-549 (1956). 



14. J. D. Watson and F. H. C. Crick: The structure of DNA. Cold Spr. Harb. Symp. 

 Quant. Biol. 18, 123-131 (1953). 



