Section 5 — Mutagenesis 



between X-irradiations and chemicals has, so 

 far, been observed. Possible mechanisms for 

 this unusual type of biological activity are 

 discussed in view of the available evidence. 



5.8. Mutation during and after Synthesis of DNA. 

 Herbert E. Kubitschek (Argonne, U.S.A.). 



In tryptophan-limited continuous cultures of 

 Escherichia coli B/l, try, the rate of caffeine- 

 induced mutation to resistance to bacteriophage 

 T5 is constant, independent of growth rate. 

 However, mutation rate is proportional to 

 growth rate for cultures limited with glucose, 

 lactate, succinate or phosphorus. These differ- 

 ent responses do not appear to be due to differ- 

 ent cellular concentrations of caffeine nor to 

 death or reversion of mutants before expression 

 of the mutant phenotype. The simplest interpre- 

 tation of the two kinds of response is that the 

 mutagen affects DNA either during or after 

 synthesis. If the mutagen acts only during the 

 formation of DNA then, as predicted by the 

 error hypothesis, mutation rate should be 

 proportional to the rate of replication of DNA, 

 and hence to growth rate. Alternatively, if the 

 mutagen acts after formation of DNA the rate of 

 mutation should be constant since DNA is 

 present in relatively constant amount. The prima- 

 ry evidence supporting this interpretation is that 

 responses to two other mutagens are in agreement 

 with expectation. There is evidence that the 

 first, ultraviolet light, acts upon DNA rather than 

 its precursors. If so, mutation rate should be 

 independent of growth rate for cultures limited 

 either with glucose or with tryptophan. This 

 result is found. For the second, 2-aminopurine, 

 mutation is expected to result from the incorpo- 

 ration of this base analog into DNA. Hence 

 mutation rate is expected to be proportional to 

 growth rate for either limiting factor. This 

 proportionality is also observed. 



Work supported by the U.S. Atomic Energy 

 Commission. 



5.9. Elective (Specific Directed) Mutation in Bacteria. 



Francis J. Ryan and Stephen D. Cetrulo 

 (New York, U.S.A.). 



The demonstration by Nagata that the 

 chromosome in synchronously dividing E. coli 

 Hfr replicates synchronously and with a polarity 

 from the hind (F containing) end allows the 



following experiment. Similarly synchronized 

 bacteria are exposed to short pulses of a base 

 analogue which is mutagenic only upon in- 

 corporation. Only those genes which are repli- 

 cating during the pulse are expected to undergo 

 induced mutation. Preliminary experiments 

 bear out this expectation. Applications of this 

 technique to genetic problems, such as mapping, 

 will be discussed. 



5.10. New Derivatives of (3-chloro- ethyl- amine as 

 Active Mutagenic Factors. S. I. Alikhanian 

 and M. Oganesian (Moscow, U.S.S.R.). 



It is known, that a number of (3-chloro-ethyl- 

 amine derivatives, such as embichin, chloram- 

 bucil and sarcolysine are highly mutagenic. 



We have studied for genetic purposes a large 

 series of previously not investigated amino acid 

 derivatives of (3-chloro-ethyl-amine, synthesized 

 in the laboratory of I. L. Knuniantz. Thirty-four 

 new compounds included two derivatives of 

 p-di (2-chlorpropyl) amine, one derivative of 

 /j-chloro-ethyl-sulfide and thirty-one derivative 

 of n-di (2-chloro-ethyl)amine. These agents 

 belong to monofunctional, bifunctional, tri- 

 functional and tetrafunctional compounds. This 

 means that all derivatives had an "attacking" 

 (3-chloro-ethyl group with the exception of some 

 derivatives having as an "attacking" 2-chlor- 

 propyl group instead of 2-chloro-ethyl group. 



From 37 compounds tested we selected seven 

 most active compounds which were studied 

 more thoroughly. Among them methyl-bis- 

 (P-chloro-ethyl)-amine (embichin), /»-propyl- 

 (bis-(3-chloro-ethyl)amine (chlorambucil), and 

 bis-((3-chloro-ethyl)-amino-phenyl-alanine (sar- 

 colysine) were studied previously with respect to 

 their mutagenic action on Neurospora, Penicilli- 

 um chrysogenum, D. melanogaster, phage T4 of 

 E. coli and other organisms. 



Compounds Nos. 6 (Ethyl ether of S-(3- 

 chloro-ethyl-dl-cysteine hydrochloride), 31 (Bis- 

 /chlorpropyl/phenylacetic acid), 32(N-formul- 

 sarcolysine), and 33 (N-acetylsarcolysine) were 

 the most active among the new compounds 

 studied by us. 



For comparative purposes highly active 

 mutagenic factors, such as ultraviolet light, 

 diethylsulfate, and ethylenimine were used. 

 Strain H-6 of Actinomyces olivaceus served 

 an as object in our experiments. The muta- 

 tions were esti mated according to three cha- 

 racteristics, that is methionine deficiency (M - ), 

 streptomycin sensitivity (S s ), and vitamin B12 

 synthesis (B12). According to the first two 

 characteristics the frequency of back mutations 



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