Bacteria: Recombination {III) 



363 



strain), and has a preferential site of attach- 

 ment near Lac (lactose). However, the Hfr 

 produced also carries F'-^ particles in the cyto- 

 plasm. 



Because of its replicability and genetic 

 variability, the male fertility factor of E. coli 

 must be considered to be composed of genetic 

 material. F is probably neither lytic nor 

 otherwise rapidly lethal to F" cells. In view 

 of this and the fact that it has a stable rela- 

 tionship with the F+ cell, it may be considered 

 a normal cellular component, when present. 

 Since it can exist and reproduce extrachro- 

 mosomally, F furnishes the first example so 

 far presented of normal extrachromosomal 

 genetic material. When F, as an autonomous 

 extrachromosomal agent, is lost, either spon- 

 taneously or after treatment with acridine 

 orange, it represents genetic material that is 

 not conserved for future generations. 



F also has the capacity to assume a regular 

 locus on a chromosome. When integrated 



into the chromosome, it behaves as an 

 ordinary chromosomal locus. In regular 

 vegetative reproduction, chromosomal F is 

 transmitted to all progeny, that is, it is con- 

 served. In conjugation, however, chromo- 

 somal F may not be conserved, since it is not 

 transmitted to the zygote with appreciable 

 frequency, except in the case of Vhf strains, 

 and even when transmitted, it may fail to be 

 integrated. 



To the genetic elements restricted to the 

 chromosome, the only type of gene discussed 

 in detail until this Chapter, we can now add 

 the male fertility factor, F, which may be 

 present or absent from the cell, and, when 

 present, may be autonomous extrachromo- 

 somally or integrated in the chromosome. 

 To such genes which can participate in the 

 cell facultatively, as extrachromosomal or 

 as chromosomal elements, the name episome 

 is given.'' 

 9 See F. Jacob and E. L. Wollman (1958). 



SUMMARY AND CONCLUSIONS 



In E. coli, there is only one female mating type, or genetic recipient (F") but several male 

 mating types, or genetic donors (F+, Hfr, Vhf), Male mating type depends upon the pres- 

 ence, location, and genotype of F. 



F is an episome. When present extrachromosomally, F is infective. When located 

 chromosomally, the ring chromosome of E. coli is opened near the locus of F. The end 

 opposite the F locus proceeds first, in the linear transfer of part or sometimes all of the 

 opened chromosome into the recipient conjugant. 



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. 



Hayes, W., "The Mechanism of Genetic Recombination in Escherichia coli,'' Cold Spr. 

 Harb. Sympos. Quant. Biol., 18:75-93, 1953; reprinted in Papers on Bacterial Ge- 

 netics, Adelberg, E. A. (Ed.), Boston, Little, Brown, 1960, pp. 268-299. 



Hayes, W., and Clowes, R. C. (Eds.), Microbial Genetics, Cambridge, Cambridge University 

 Press, 300 pp., 1960. 



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

 Acad. Sci. (Paris), 247:154-156, 1958; translated and reprinted in Papers on Bacterial 

 Genetics, Adelberg, E. A. (Ed.), Boston, Little, Brown, 1960, pp. 398-400. 



