Section 5 — Mutagenesis 



is independent of time ("dose rate") at the 

 higher concentrations. At the lowest concen- 

 trations used, there is a decreased response to 

 a given dose. 



1. Consult: Kolmark and Kilbey, Z.f. Verer- 

 bungslehre 93, 356-365, 1962, regarding 

 techniques. 



5.19. Mutation and Crossing-over Induced by Mono- 

 and Bifunctional Alkylating Agents. G. Mor- 

 purgo (Rome, Italy). 



The ability of methyl bis ((3-chloroethylamine, 

 2-chlorotriethylamine hydrochloride, diepoxybu- 

 tane and ethylene oxide) in inducing mutation 

 and mitotic crossing-over in a diploid strain of 

 Aspergillus nidulans has been tested. 



Mono- and bifunctional compounds are 

 equally active in inducing mutation. Only 

 bifunctional compounds are able to induce high 

 frequency of somatic crossing-over. These 

 effects on crossing-over can be attributed to the 

 cross-linkage of non sister chromatids. 



5.20. Genetic Analyses of Photo-reactivation, Dark- 

 reactivation and Resistance to Ultraviolet Light 

 in Escherichia coli. P. van der Putte and 

 A. Rorsch (Rijswijk The Netherlands). 



The genetic constitution of mutations in 

 Escherichia coli which affect the radiation 

 sensitivity of the strain has been studied. One 

 mutation leads to loss of the tendency to form 

 long filaments after u.v. irradiation, a second 

 to loss of the ability to repair u.v. lesions in the 

 DNA of the cell in the dark (dark-reactivation) 

 and a third mutation to loss of the ability 

 to repair u.v. lesions by subsequent irradiation 

 of the cell with visible light (photo-reactivation). 



By conjugation experiments with auxotrophic 

 mutants it is proved that all three properties are 

 chromosomally determined and may be located 

 as distinct markers on the bacterial genome. 

 Methods to screen large numbers of recombi- 

 nants for the markers which affect the radiation 

 sensitvity of a strain will be described. The 

 results will be published in full in the Biochim. 

 Biophys. Acta. 



5.21. Reactivation of U.V. Irradiated Escherichia coli 

 K-12 (A) by Treatment with EDTA. Renana 



Ben-Gurion (Ness-Ziona, Israel). 



When lysogenic bacteria are irradiated, the 



prophage genome passes from a state of repres- 

 sion to an active state, phages are being pro- 

 duced, and the lysogenic bacteria are killed in 

 this process. It appears, therefore, that induction 

 (a process as yet not fully understood) renders the 

 lysogenic bacteria more sensitive to irradiation 

 than their nonlysogenic derivates. Because of the 

 higher sensitivity of lysogenic cells to irradiation, 

 these organisms could perhaps be suitable tools 

 for the study of irradiation effects. 



When the lysogenic bacterium Escherichia coli 

 K-12 (A) (strain 169) was irradiated with ultra- 

 violet light and then transferred to a medium 

 containing EDTA, this resulted in a partial 

 reactivation of the lysogenic bacteria. The num- 

 ber of survivals was increased and the production 

 of phage decreased, as compared with the irra- 

 diated controls. The composition of the bacterial 

 growth medium, as well as that of the medium 

 to which the bacteria were transferred after 

 irradiation, had a marked effect both on the 

 number of surviving cells and on the reactivation 

 resulting from the treatment with EDTA. 



5.22. X-ray and Ultraviolet Light Mutagenesis in a 

 Threonine Requiring Escherichia coli K12 stud- 

 ied by Recombination Techniques. T. Kada 

 and H. Marcovich (Paris, France). 



During the mating process in E. coli K12, the 

 chromosome of the male cell (Hfr) is transferred 

 into the female (F ) without any detectable 

 amount of cytoplasmic material. This system, the- 

 refore, is a workable one for determining wheth- 

 er the initial step in X-ray or u.v. mutagenesis is 

 a cytoplasmic or nuclear one. This work deals 

 with crosses between E. coli Hfr thr~33leu + sen- 

 sitive to T6 phage and E.coli F-thr _ 33leu- resistant 

 to T6 phage. Having irradiated the male before 

 mating with the female, we scored the reversion 

 to threonine independence among the recombi- 

 nants possessing the resistance to T6 and having 

 received in addition the leu+ character. The thr 

 and leu determinants are closely linked, and leu 

 serves here as a scoring factor which assures that 

 the thr region of the male chromosome has been 

 injected into the female. When the male is irra- 

 diated with X-rays, the mutant character can be 

 immediately transferred to the zygote. With 

 u.v. irradiation, no such immediate transfer is 

 seen. This transfer takes place only afterwards, 

 increasing with time up to 100 per cent in 24 hr 

 culture in broth. In reciprocal irradiation in- 

 volving the female, it appears that the male 

 genetic material is mutated if injected in a u.v. 

 irradiated female, but not if X-ray is used. These 



62 



