SiteSpecific Recombinations

1
Site-Specific Recombinations

• Integrases
• Resolvases
• Invertases

2
Site-Specific Recombinations

• Integrases
• Promotes integration of two DNA molecules
• Recognizes specific DNA sequences
• attP in lambda phage

3
Site-Specific Recombinations

• Resolvases
• Promotes recombination within the same DNA
  molecule
• Recognizes specific DNA sequence res
• Resolve the co-integrate

4
(No Transcript)
5
(No Transcript)
6
Regulation of Transposition

• Transposition may be regulated by methylation

GAT C
CT A G
Replication
GAT C
CT AG
GA T C
CT AG
hemimethylated
7
Regulation of Transposition

• Transposition may be regulated by methylation

tnp
GAT C
CT AG
-10
Fully methylated, transcription of tnp is
poor. Hemi-methylated, transcription of tnp is
high.
8
Regulation of Transposition

• Transposition may be regulated by methylation

IS
GAT C
CT AG
-10
Transposase binds to the inverted repeats more
efficiently when the site is hemimethylated.
9
Regulation of Transposition

• Transposase preferentially acts in cis.
• Transposase is very unstable
• It prefers acting on its own transposon
• The efficiency of transposition will decrease to
  act on distance transposons

10
Regulation of Transposition

• Transposase may be repressed in trans

average
0.2 copies per cell
tnp
5 copies per cell
Anti-sense RNA
Live longer