2. 1. General or homologous recombination : occurs
between DNA molecules of very similar sequence,
such as homologous chromosomes in diploid
organisms.
Is an integral part of the complex process
of meiosis in sexually reproducing organisms. Results
in crossing over.
In Bacteria: recombination during F-factor mediated
conjugal transfer of parts of chromosomes.
In Bacteriophages Recombination between two
phage during a mixed infection of bacteria
Breaking and rejoining of two parental DNA molecules
to produce new DNA molecules
Genetic recombination
3. 2. Illegitimate or nonhomologous recombination
occurs in regions where no large-scale sequence
similarity is apparent, (i.e due to translocations
between different chromosomes or deletions
that remove several genes along a chromosome).
3. Site-specific recombination occurs between
particular short sequences (about 12 to 24 bp)
present on otherwise dissimilar parental
molecules. Eg. integration of bacteriophages.
4. 3. Replicative recombination: generates a new
copy of a segment of DNA. New DNA
molecules carry genetic information from both
parental molecules.
Ex: transposable elements, Mu Phages.
5.
6. Mechanism of Recombination
• Endonuclease cuts DNA in the middle of a strand,
and nicks one strand of the donor DNA.
• This nicked strand is separated from the other
strand by proteins with helicase activity
• The resulting single-stranded segment binds to
SSbps and then RecA. This results in a complex
that promotes base pairing with the
complementary sequence in the recipient DNA
molecule.
• This base pairing in turn displaces the other
strand of the recipient DNA molecule (strand
invasion).
• Heteroduplex regions, with each strand
originated from a different chromosomes.
• Resolvase (RuvC protein): specifically cleave
Holliday intermediates have also been isolated
from bacteria and yeast.
• COMPLEMENTATION
7. Rec A Protein
• A 38 kilodalton protein essential for the repair and maintenance ofDNA.
• Activated during DNA Damage
• The RecA protein binds strongly to ssDNA to form a nucleoprotein
filament.
• Has more than one DNA binding site, and thus can hold a both the
strands together.
• This feature makes it possible to catalyze a DNA synapsis reaction
between a DNA double helix and a complementary region of single
stranded DNA.
8. Watson, J.D, Baker T.A, Bell, S.P, Gann, A., Levine, M and Losik R ( 2004).
The replication of DNA, Molecular` Biology of the Gene, (5th ed).
Perason Education Inc. Ch.8 (181-233).
Madigan, M.T, Martinko, J.M, Bender, K.S, Buckley, D.H and Stahl, D.A
.(2015). Molecular Microbiology. Brock Biology of
Microorganisms.(14thed) Perason Education Inc. Ch.4 (107-135).
Madigan, M.T, Martinko, J.M, Bender, K.S, Buckley, D.H and Stahl, D.A
.(2015). Genetics of Bacteria and Archaea. Brock Biology of
Microorganisms. .(14thed) Perason Education Inc. Ch.10(291-301)
Watson, J.D, Baker T.A, Bell, S.P, Gann, A., Levine, M and Losik R ( 2004).
The Mutability and Repair of DNA, Molecular` Biology of the Gene
(5th ed) , Perason Education Inc. Ch.9 (235-258).
Weaver. R.F (2002) The Transcription Apparatus of Prokaryotes. Molecular
Biology (2nd ed). The McGraw−Hill Ch.6 (139-266)
Weaver. R.F (2002) DNA Replication I: Basic Mechanism and Enzymology.
Molecular Biology (2nd ed). The McGraw−Hill Ch.20 (648-790)
References
9. Dale, J.W and Park S.F (2004). Nucleic Acid Structure and Function,
Molecular Genetics of Bacteria (4th ed). John Wiley & Sons. Ch.1 (1-
33).
Dale, J.W and Park S.F (2004). Mutation and Variiation, Molecular
Genetics of Bacteria (4th ed). John Wiley & Sons. Ch.2 (37-62).
Dale, J.W and Park S.F (2004). Gene Transfer, Molecular Genetics of
Bacteria (4th ed). John Wiley & Sons. Ch.6 (165-187)
References
