Chapter 11 Transposition and Site-Specific Recombination 29 September and 1 October, 2004
Overview • Conservative Site-Specific Recombination (CSSR) may involve insertion, deletion, or inversion of DNA sequences. • Site-specific recombinases have a mechanism that includes a DNA-protein covalent intermediate. • CSSR may be regulated by the presence or absence of accessory proteins. • Resolvases are CSSR recombinases that disentangle circular chromosomes. • Transposons move using recombination pathways. • Transposons may be autonomous or nonautonomous. • DNA transposons and viral-like retrotransposons move via a cut/paste mechanism. • Retrotransposon movement involves reverse transcription. • Some transposons regulate copy number or control target site selection through the use of proteins or antisense RNA. • V(D)J recombination uses regulated, specific recombination to generate immune diversity.
Recombination and Transposition
CSSR: Prophage Insertion
Three Classes of CSSR
Recombinase Recognition Sites
Mechanism of Cre Recombinase
Lambda integration requires architectural proteins.
lInt and IHF stabilize bent DNA.
Hin inversion requires Fis bound at an enhancer.
Resolvases disentangle circular DNAs after replication.
FtsK Regulation of the Xer Resolvase Mechanism
FtsK is present at the division closure site.
Conservative and Replicative Transposition
Transposons in Several Genomes
Types of Transposons
Cut and Paste Transposition
Three Mechanisms for Cleaving the Nontransferred Strand
DNA Transposases and retroviral integrases are members of the same protein superfamily.
LINE poly-A Retrotransposon Movement
Tn10 achieves antisense copy control by overlapping promoters.
Antisense Copy Control
Tn10 transposase promoter is active only when hemimethylated.
MuA and MuB participate in selecting Mu transposition target sequences.
MuA disrupts MuB assembly, conferring transposition target immunity.
Clustered Integration of Yeast Ty Elements
Recombination Signal Sequences
V(D)J Recombination Mechanism
LINES and SINES Again?