Section 3 — Molecular and Microbial Genetics 



of the information determining lysogenization 

 will be presented. (3 ) 



The possible interpretation of the process of 

 transformation of lysogenization and immunity 

 in line with current ideas of the specific repressor 

 control mechanism will be discussed. 



3. B. Gyorffy, K. Hatnay and I. Kallay, to 

 be published in Acta Microbiol. Hung., 1963. 



3.29. Bacteriophage Transformation. G. Veldhuisen, 



R. A. OOSTERBAAN, P. H. POUWELS, H. S. 



Jansz and J. A. Cohen (Rijswijk (Z.H.), 

 The Netherlands). 



Transformation of bacteriophage T4 with 

 purified DNA has been demonstrated earlier/ 1 ) 

 Spheroplasts of Escherichia coli B were mixed 

 with a purified DNA preparation obtained from 

 T4rII+ phages and infected with urea-disrupted 

 particles of a T4rII-mutant. By plating on E. coli 

 K 112-12 (A h) # 3 and on E. coli B the yield of 

 transformants and total phage yield were deter- 

 mined respectively; the rll+/rll ratio (transfor- 

 mation frequency) varied between 10 _6 to 10 T for 

 native DNA using a concentration of approx. 

 lOug/ml. 



We wish to report some further results: 



(1) More reproducible results were obtained 

 using spheroplasts prepared from cells that 

 were grown to exhaustion in minimal medium 

 plus 0.04 per cent glucose. 



(2) Heating of the DNA preparation (5 min 

 at 100° C) in 0.01 m phosphate buffer pH7 

 increases the transformation frequency and 

 also the total number of transformants by 

 about 5-10 times. 



(3) The increase in biological activity after 

 heating follows the increase in optical density 

 at 260 mu measured after rapid cooling of 

 samples that had been heated at various 

 temperatures. 



(4) DNA molecules fragmented mechanically 

 to a weight average molecular weight of 

 about 275,000 were still biologically active. 

 Degradation by means of limited amounts 

 of DNA-ase gave similar results. 



(5) The transformation of T4rII mutant is 

 equally effective with DNA prepared from 

 T2, T4 and T6. Among the transformants, 

 obtained using T4rII+-DNA and disrupted 

 T6rII, some are able to grow on B/6 suggest- 

 ing that other T4 markers may be inherited. 



3.30. Electronmicroscopic Studies of Cells and DNA 

 Molecules during the Genetic Transformation 

 of Bacteria. Alexander Tomasz and Wal- 

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



Competence: The ability of certain bacterial 

 cells to absorb highly polymerized biologically 

 active DNA molecules in the process of genetic 

 transformation must necessarily involve the 

 adsorption of the molecules to the cell surface 

 and their eventual penetration through the 

 bacterial surface structures. Attempts are being 

 made to study this process in the electron 

 microscope. Conditions will be described under 

 which the method of Kleinschmidt (1 ) can be 

 adapted to visualize DNA strands in association 

 with competent bacteria. 



The particular question asked is whether there 

 is any localization on the bacterial surface for 

 the adsorption and entry of DNA molecules. 

 Thin sections of pneumococcal cells^ revealed 

 the existence in these cells of unusual membrane- 

 like structures which were often attached to the 

 developing septum of dividing cells. In view of 

 the suggested correlation between the division 

 state of the cells and their competence 13 ' this 

 observation directed our attention to the septum 

 of dividing cells as possible sites for the entry of 

 DNA molecules into the cell. 



1. Cf. Veldhuisen et al., Biochim. Biophvs. 

 Acta 61, 630, 1962. 



1. Z.f. Naturf. 16b, 730, 1961. 



2. Publication under preparation — Drs. J. Ja- 

 mieson and E. Ottolenghi. 



3. Hotchkiss, Proc. Nat. Acad. Sci. U.S. 40, 

 49, 1959. 



3.31. Some Factors affecting the Frequency of 

 Streptomycin Resistant Transformants through- 

 out the Evolution of Competency. M. Ko 



houtova, H. Kopecka, and J. Konicek. 

 (Prague, Czechoslovakia). 



Two different transformation media for the 

 transformation of the streptomycin sensitive 

 strain of Pneumococcus (PMS1IB) to the strepto- 

 mycin resistant one were used. (1) Neopepton- 

 heart infusion broth enriched with some ingre- 

 dients and (2) the so-called NS-medium (H. E. 

 Taylor). With both media we obtained similar 

 results as in the type-transformation experi- 

 ments previously performed in our laboratory, 

 concerning the presence of salts with monovalent 

 cations and their support in a good transfor- 

 mation yield. 



The competent recipient culture was diluted 

 into the appropriate transformation medium 



28 



