LETHAL ACTION OF X-RAYS IN E. roli K12 181 



DISCUSSION 

 ZHUKOV-VKKEZHNicov: It seems to me that additional proofs nvr ncMMlcd that 

 you worked with multinucleate strains of the Esclnnicha coll culture. 



MARCOVICH: First, the method of staining according to Feulgen has shown tlie 

 presence of two or three nuclear bodies. Secondly, if you are working with ^^^P- 

 labelled bacteria and allow transmutation to occur, then suixival cuives to radio- 

 active decay will correspond to nuiltiple-type inactivation, which coiTelate with 

 the number of bodies stained positively by Feulgen. Finally, if you make 

 crosses, as I have already said, between "male" and "female" strains, and obtain 

 recombination and then remove the "male", you would see that this cell remains 

 normal, because it transmits to the zygote only a part of its genetic material, 

 whereas an identical part of this material remained in it. 



ZHUKOV-VEREZHNicov: What is the largest number of nuclei, which you could 

 distinguish morphologically in one cell in the Escherichia coli sti'ain? 



MARCOVICH : iTp to four in one cell which is preparing to divide. Speaking gener- 

 ally three nuclei may also be encountered, but the number most often met with is 

 two. Experiments aimed at determining the exact shape of the survival curve 

 are such that two nuclei are found with absolute certainty. 



alichanian: I listened to your very interesting and original report with great 

 pleasure. I am interested in a question bearing on the technique of your work. 

 When you were preparing suspensions for inoculation and obtaining recombinants 

 did you take into account the relative proportions of the components, i.e. the 

 parent "male" and "female" cells? 



MARCOVICH: Yes, we did. The best method is to introduce one "male" per ten 



"females", in order to be quite sure that conjugation w^ould occur for all the 



"males". 



alichanian: Did you use in your work F± and F= or Hfr = forms? 



MARKOViCH : It may be carried out with Hfr forms. 



alichanian: I want once again to emphasize the fact that your work makes it- 

 possible to evaluate similar curves on an entirely new basis. This work allows uS 

 to decipher dominant and lethal mutations and to determine whether there is 

 death of whole nuclei or some cell damage in general. 



gray: When crossing occurs there is probably some locus in tlie chromosome 

 which is first transferred from male to female, and if this is so, then some of the 

 mutations arising during irradiation, would escape analysis. 



MARCOVICH: Yes, this is so. If you calculate the target area for this locus, it 

 would be very small. About 1 :200 of all the combinations escape, and this is not 

 much. 



GRAY : It seems to me that it is important to know what becomes of these chromo- 

 somes, because damage may be distributed unequally throughout the chromo- 

 some's length. 



MARCOVICH : X-rays did not inactivate in these experiments any chromosome locus 

 as such. It was possible only to study the probability of the manifestation of a 

 given locus in the recombinant. Loci for threonine and leucine are found very 



