Section 3 — Molecular and Microbial Genetics 



tion-rate was achieved only by addition of CdR. 

 In modified SS-medium (containing normal 

 Bacto casamino acids instead of the vitamin- 

 free preparation) FU does not induce but still 

 shows its bacteriocidic activity. Investigations 

 with FU in SS-medium supplemented with 

 vitamins are in progress. Preliminary results 

 show that several vitamins are apparently able 

 to reduce or to abolish the inducing action of 

 FU without interfering with its bacteriocidic 

 activity. 



These results suggest that the halogenated 

 pyrimidines used exert their inducing action 

 by a rather unspecific disturbance of (nucleic 

 acid) metabolism of the lysogenic cells so 

 treated. There are no reasons for assuming a 

 direct action of these agents on the deoxyri- 

 bonucleic acid of the prophages or on DNA 

 synthesis. Other experiments on the inducing 

 effect of ultraviolet- and X-rays on BU-labelled 

 lysogenic cells indicate that ultraviolet rays too 

 do not induce by a direct action on DNA. 



this prophage, photoreversal of induction is 

 less for a given dose of u.v. than in wild-type 

 lambda. But if doses giving the same surviving 

 fraction of lysogenic bacteria are compared, 

 the u.v. -sensitive prophage is at least as suscep- 

 tible to photorepair as wild-type lambda. 

 Acridines and methyl purines do not enhance 

 u.v. induction of u.v. -sensitive lambda. These 

 results can be attributed to the inability of the 

 u.v. -sensitive phage to undergo dark repair of 

 u.v. damage to the nucleic acid region that 

 controls production, or acceptance, of repressor. 

 When lysogenic bacteria are forced to incor- 

 porate 5-bromouracil, their prophages become 

 more sensitive to u.v. induction. Acridines and 

 methyl purines enhance u.v. induction in such 

 bacteria, but there is no photoreversal of induc- 

 tion. Additional data indicate that the photo- and 

 dark repair systems act on the same u.v. dama- 

 ged sites in nucleic acid, but act independently. 



The paper will be published in Acta Biologica 

 et Medica Germanica (Berlin). 



3.27. Genetic and Environmental Factors affecting 

 Prophage Induction. Margaret Lieb (Cali- 

 fornia, U.S.A.). 



A prophage has one or more genes whose 

 product(s) apparently repress the function of 

 other genes involved in phage replication. 

 Although the repressor may be a protein, DNA 

 and/or RNA are probably the sites affected by 

 many treatments that induce phage develop- 

 ment in lysogenic bacteria. In some lysogenic 

 bacteria, the phage system(s) blocked by the 

 hypothetical repressors are extremely sensitive 

 to induction (derepression) by u.v. light. Methyl 

 purines and acridines, which enhance mutation 

 in u.v. -irradiated bacteria, also enhance induc- 

 tion of lambda prophage replication. These 

 substances combine with DNA and presumably 

 distort the molecules in previously denatured 

 regions. In this way, they either prevent reversal 

 of u.v. damage by a dark repair system in the 

 bacterium, or otherwise increase the probability 

 that an absorbed u.v. quantum will result in 

 mutation or induction. These substances do not 

 enhance prophage induction by agents other 

 than u.v. and have little effect on killing of non- 

 lysogenic bacteria. 



We have also studied a lambda prophage that 

 is unusually sensitive to induction by u.v. For 



3 78. Transfer of Information determining Lysogeni- 

 zation in Bacteria by Transforming DNA. 

 B. Gyorffy (Budapest, Hungary). 



Immunity to subsequent superinfection with 

 closely related phages to that carried as prophage 

 is a general property of lysogenic bacteria. This 

 immunity could be transferred by the DNA 

 isolated from the lysogenic strain 41/63-3/ of 

 Rhizobium meliloti into the sensitive strain 41, 

 on which a brief preliminary report was already 

 published/ 1 ) Further experiments were per- 

 formed, involving bacterial DNA and phage 

 DNA labelled with 32 P and/or 14 C, and transfor- 

 mations with DNA isolated from temperate 

 phages, respectively, to gain more insight into 

 the process of transfer of the capacity to estab- 

 lish the lysogenic complex in the recipient bac- 

 teria after transformation. The results obtained 

 presenti reliable evidence to separate the 

 transforming efficiency of the bacterial DNA 

 and prophage DNA, respectively, involved in the 

 transformation of immunity to superinfection 

 by the DNA isolated from the lysogenic strain/ 2 ) 



Studies on this line also are in progress with 

 Bacillus subtilis, where DNA from the lysogenic 

 strain 3NT is used to transform the recipient 

 strain 168, and the results on transformation 



1. K. Szende, T. Sik, F. Ordogh and B. Gyorf- 

 fy, Biochim. Biophys. Acta 47, 215-217, 1961. 



2. T. Sik, B. Gyorffy, K. Szende and M. Cza- 

 ko, to be published in Acta Microbiol. Hung., 

 1963. 



27 



