Bacterial Episomes and Genetic Recombination 361 



F is transferred to the F^ col I conjugant, phages, ,; F factors, RTF factors, and col fac- 

 and col I is transmitted to the F + col~ con- tors. It is still too early, however, to make 

 jugant with high efficiency. However, when any kind of definite suggestion as to the pre- 

 F+ col I is crossed with F~ col~ , col I is cise nature of the evolutionary interrelation- 

 transferred at a low rate, so that F interferes ships, if any, among these various types of 

 with transfer of col I from the same parent. episomal elements. 



The preceding shows a number of simi- ,. „ , „ „ „ _ 



, . . r . , ° See also E. Seaman, E. Tarmy and J. Marmur 



lanties among temperate and virulent (1964). 



SUMMARY AND CONCLUSIONS 



A two-directional flow of F and chromosomal genetic material occurs between extra- 

 chromosomal F and the chromosome. Chromosomal markers carried by free F retain 

 their capacity for replication and phenotypic action. 



F', other F-merogenotes, RTF factors, and some col factors behave like episomes. 



Col factors have several characteristics in common with F and the provirus stage 

 of temperate phages. Their products, colicins, resemble the lethal, tail-tip protein of 

 virulent phages. Accordingly, it is possible that F, temperate phage, virulent phage, 

 and col factors are related in evolution. 



Certain bacterial episomes promote their own transfer and/or transfer of other genetic 

 material via conjugation. In Salmonella, col I promotes the transfer of col El which. 

 in turn, promotes the transfer of the chromosome. RTF promotes the transfer of 

 linked drug resistance markers and can inhibit certain promoter functions of F. 



Since they can initiate conjugation, F and its derivatives, col I, and RTF are sex 

 factors. 



REFERENCES 



Adelberg, E. A., and Burns, S. N., "Genetic Variation in the Sex Factor of Escherichia 

 Coli," J. Bact., 79:321-330, 1960. Reprinted in Papers on Bacterial Genetics, 

 Adelberg, E. A. (Ed.), Boston: Little, Brown, 1960, pp. 353-362. 



Campbell, A. M., "Episomes," Advances in Genetics, 11:101-145, 1962. 



Clark, A. J., and Adelberg, E. A., "Bacterial Conjugation," Ann. Rev. Microbiol., 

 16:289-319, 1962. 



Fredericq, P., "On the Nature of Colicinogenic Factors: A Review," J. Theoret. Biol., 

 4:159-165, 1963. 



Goebel, W. F., "The Chromatographic Fractionation of Colicine K," Proc. Nat. Acad. 

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Hayes, W., The Genetics of Bacteria and their Viruses, New York: J. Wiley & Sons, 

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lacob, F., and Wollman, E. L., "Episomes, Added Genetic Elements" (in French). 

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 pp. 398-400. 



Maas, R., "Exclusion of an F Lac Episome by an Hfr Gene," Proc. Nat. Acad. Sci., 

 U.S., 50:1051-1059, 1963. 



Seaman, E., Tarmy, E., and Marmur, J., "Inducible Phages of Bacillus subtilis," Bio- 

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Watanabe, T., "Infectious Heredity of Multiple Drug Resistance in Bacteria," Bact. 

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