Hfr Conjugation and Chromosomal Transfer

• Conjugation is the transfer of chromosomal material from one bacterial cell to another by direct cell-to-cell contact was discovered in 1946 by Lederberg and Tatum”,

(Adelberg & Pittard, 1965)

• F plasmid is a piece of DNA exist on its own in the cytoplasm.

• The F plasmid is considered to be an episome which may become integrated into the main chromosome.

• When the F genes become integrated into the chromosome, the cell is said to be Hfr (High Frequency of Recombination).

Hfr bacteria Possess the entire F episome integrated into the bacterial 

genome.

F+ bacteria Possess F factor as a plasmid independent of the bacterial genome. The F plasmid contains only F factor DNA and no DNA from the bacterial genome.

F' (F-prime) bacteria Formed by incorrect excision from the chromosome, resulting in F plasmid carrying bacterial 

sequences that are next to where the F episome has been inserted

F− bacteria Do not contain F factor and act as 

the recipients.

The Hfr chromosome, originally circular, unwinds and is transferred to the F− cell in a linear fashion.(Griffiths et al,2000)

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References:

• Adelberg,  E.  A.,  &  Pittard,  J.  1965.  Chromosome  Transfer  in  Bacterial Conjugation. Bacteriological Reviews, 29(2), 161–172.

• Griffiths,  A.J.F.,  Miller,  J.H.,  Suzuki,  D.T.,  et  al.2000.Bacterial  Conjugation.  An Introduction  to Genetic Analysis.  7th  edition. New York,NY:W.H.  Freeman. Retrieved from http://www.ncbi.nlm.nih.gov/books/NBK21942/

• Gross,J.D., Caro,L.G.1966. DNA transfer in bacterial conjugation. Journal of Molecular Biology. Volume 16,Issue 2,pp269-284.

•   Friedrich  Bonhoeffer.  1966.  DNA  transfer  and  DNA  synthesis  during  bacterial conjugation. Zeitschrift für Vererbungslehre.Volume 98, Issue 2 , pp 141-149 

• Sarathy,P.V.,  Siddiqi,O.  1973.  DNA  synthesis  during  bacterial  conjugation:  II.  Is  DNA replication  in  the  Hfr  obligatory  for  chromosome  transfer?  Journal of Molecular Biology. Volume 78, Issue 3,pp 443-451.