Viruses: Recombination in Bacteriophage (/) 389 



SUMMARY AND CONCLUSIONS 



T-even phages are virulent in E. coli. Their morphology and lytic cycle are discussed, 

 their genetic material identified chemically as DNA. Following multiple infection with 

 phages carrying different genetic markers, genetic recombinants are found among the 

 progeny. 



From the results of such phage crosses a recombination map can be constructed in which 

 the genes are arranged linearly. Recombinant phages are often also diploid for a short 

 region between the recombinant markers. Both phage recombination and partial diploidy 

 may sometimes be the consequence of a copy-choice mechanism of DNA replication during 

 which there has been a switching of the templates utilized in the making of partial replicas. 

 Sometimes, if not always, phage recombination involves parental strands which have 

 broken. 



REFERENCES 



Brenner, S., Streisinger, G., Home, R. W., Champe, S. P., Barnett, L., Benzer, S., and Rees, 

 M. W., "Structural Components of Bacteriophage," J. Mol. Biol., 1:281-282, 1959. 



Hershey, A. D., and Chase, M., "Genetic Recombination and Heterozygosis in Bacterio- 

 phage," Cold Spr. Harb. Sympos. Quant. Biol., 16:471-479, 1951; reprinted in Papers 

 on Bacterial Viruses, Stent, G. S. (Ed.), Boston, Little, Brown, 1960, pp. 179-192. 



Hershey, A. D., and Chase, M., "Independent Functions of Viral Protein and Nucleic Acid 

 in Growth of Bacteriophage," J. Gen. Physiol, 36:39-54, 1952; reprinted in Papers 

 on Bacterial Viruses, Stent, G. S. (Ed.), Boston, Little, Brown, 1960, pp. 87-104. 



Kellenberger, G., Zichichi, M. L., and Weigle, J. J., "Exchange of DNA in the Recombi- 

 nation of Bacteriophage X," Proc. Nat. Acad. Sci., U.S , 47:869-878, 1961. 



Krakow, J. S., Kammen, H. O., and Canellakis, E. S., "The Incorporation of Ribonucleo- 

 tides into Terminal Positions of Deoxyribonucleic Acid," Biochim. et Biophys. Acta, 

 53:52-64, 1961. 



Meselson, M., and Weigle, J. J., "Chromosome Breakage Accompanying Genetic Recombi- 

 nation in Bacteriophage," Proc. Nat. Acad. Sci., U.S., 47:857-868, 1961. 



QUESTIONS FOR DISCUSSION 



42.1. Is the hole in the tail of T-even phages large enough for the passage of one or of two 

 double helices of DNA? Explain. In what respect does your answer bear on the 

 manner of entry of phage DNA into a bacterial host? 



42.2. What are the advantages of studying phages using bacteria growing on solid, rather 

 than in liquid, culture medium? 



42.3. Do you think it would be feasible to study the genetic basis for different morphological 

 or for different protein components of a phage? Explain. 



42.4. If a phage is virulent in one strain of bacteria and not in another, is it temperate for 

 the latter? Explain. 



42.5. What is meant by a phage cross? Describe how you would know that you made one. 



42.6. Are the genes which show recombination always diploid in a recombinant phage? 



42.7. Does the fact that complete progeny phages are liberated after naked DNA from 

 0X174 infects a protoplast mean that all the information for making 0X174 DNA 

 and 0X174 protein is contained in the phage's DNA? Explain. 



42.8. Are the hypotheses of phage recombination by breakage and by copy-choice mutually 

 exclusive? Explain. 



