Section 3 — Molecular and Microbial Genetics 



3.16. Recombination of Purified DNA of Bacterio- 

 phage OX 174 in Spheroplasts. H. S. Jansz, 

 C. van Rotterdam and J. A. Cohen (Rijswijk 

 (Z.H.), The Netherlands). 



The DNA-spheropIast system^ 1 ) for the deter- 

 mination of the biological activity of purified 

 DNA of bacteriophage OX 174 was employed in 

 a biochemical approach to the elucidation of 

 the mechanism of gene action. In order to study 

 genetic recombination in this system phage and 

 bacterial mutants were derived from OX 174 

 wild type (Oo) and its host E. coli C (Co) ac- 

 cording to the method of D. Pfeifer/ 2 ) 



0o is designated genetically as hl+h2+ indicat- 

 ing that it is able to be adsorbed to and to infect 

 Co but not the Oo resistant bacterial strains CI 

 and C2. Ol (hi h2 + ) is able to infect Co and 

 CI but not C2. 02 (hi h2) is able to infect Co, 

 CI and C2. 03 (hl+h2) is able to infect Co but 

 not CI and C2. In a cross 03 x 01 recombi- 

 nants 02 were obtained (recombination fre- 

 quency 10 A ). The DNA's isolated (using phenol 

 extraction) from purified batches of Ol and 03 

 were infectious to spheroplasts of E. coli 

 K12, producing approximately 10 7 phages/ml. 

 Mixed infection of spheroplasts of E. coli 

 K12 with DNA's from Ol and 03 produced 

 approximately 10 3 recombinants 02. The effects 

 of u.v. -irradiation and chain scission by DNAse 

 of one of the parental DNA's on infectivity and 

 ability to form recombinants were studied. 

 U.V. irradiation causing a fall in infectivity of 

 DNA down to 5 per cent of its original value 

 did not weaken its efficiency in giving rise to 

 recombinants. However, chain scission of 

 03-DNA by DNAse corresponding to an aver- 

 age of 3 hits per molecule destroys its recombining 

 faculty. 



1. Cf. G. D. Guthrie and R. L. Sinsheimer, 

 J. Mol. Biol. 2, 297, 1960. 



2. Z.fiir Vererbungslehre 92, 3, 1961. 



3.17. The Response of Mutants of the Bacteriophage 

 f 2 to a Bacterial Suppressor Gene. Norton D. 

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



Garen and Siddiqi have isolated a suppressor 

 gene for certain alkaline phosphatase negative 

 mutants of the bacterium Escherichia coli. This 

 same suppressor gene can also suppress specific 

 mutants of the "r2" type of the bacteriophage 

 T4 (Benzer and Champe). The assumption is 

 that this suppressor gene can work on mutants 

 in many different cistrons. 



Following nitrous acid treatment of the bac- 

 teriophage f2, we have obtained mutants which 

 respond to this same suppressor gene. These 

 phage mutants are being studied for their 

 effects upon the bacteria without the suppressor 

 gene. If, as supposed, mutations which respond 

 to this suppressor can occur in all cistrons, by 

 determining at what stage in their life cycle these 

 mutants are blocked we can infer the genetic 

 functions of the phage. The determinations in- 

 clude the production of new enzymes, infective 

 RNA, phage coat protein and phage particles. 

 In addition, RNA from the mutants is added to 

 E. coli extracts and the nature of the protein 

 products it stimulates determined. 



3.18. Studies on Plaque Mutants of the RNA Phage 

 fr. F. Kaudewitz and P. Knolle (Berlin- 

 Dahlen, Germany). 



Phage fr is related to the RNA phages descri- 

 bed by Loeb and Zinder. f 1 ) Its physical charac- 

 teristics have been described by Hoffmann- 

 Berling.( 2 ' The occurrence of plaque-size mutants 

 has been reported in phage suspensions treated 

 with nitrous acid (Kaudewitz and Knolle. ( 3 ) 

 Turbid mutants have been obtained by the same 

 method. These mutants are stable upon cloning. 

 They are inactivated by wild type fr antiserum, 

 their burst size is smaller than that of the wild 

 type phage. The infection of cells of Escherichia 

 coli K-12 strains by these mutants is inhibited 

 by RNase as is the infection by phage fr. The 

 analysis of recombination experiments obtained 

 from mixed infections involving a number of 

 different mutants of this type will be presented. 

 The data will be published in full in the Zeit- 

 schrift fur Vererbungslehre. 



1. T. Loeb and N. Zinder, Proc. Natl. Acad. 

 Sci. 47, 282, 1961. 



2. H. Hoffmann-Berling, Z. Naturforschg.,'m 

 press. 



3. F. Kaudewitz and P. Knolle, Nature, in 

 press. 



3.19. Host-range Mutations of the Bacteriophage 

 0X-174 and the Specificity of Its Host E. coli. 



G. A. van Arkel and J. H. van de Pol 

 (Utrecht, The Netherlands). 



The host-range phenotype provides a useful 

 tool in genetic studies with bacteriophage 0X- 

 174, which, because of the single-strandedness 



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