BCHM 218 Study Guide - Quiz Guide: Exonuclease, Reverse Transcriptase, Retrotransposon
7 Dec 2015
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Document Summary
Each ssr system consists of a short unique dna sequence (20-200bp) and a recombinase (acts specifically at the sequence: does not require extensive homology at recombination sites. Back mechanism of deletion: ssr systems use either tyr or ser residue as the key nucleophile in the active site, steps overall: site. A pair of recombinases recognize and bind to each recombination. Two come together to form a synaptic complex (4 recombinase subunits, 2 aligned cores) Recombinase subunits cleave dna at recombination sites: steps with tyr nucleophile (depicted in image below) One strand in each site is cleaved and 1 recombinase subunit becomes covalently linked to the dna at each site through a phosphotyrosine bond (ensuring minimal free energy change) The cleaved dna strands are rejoined to form a holliday intermediate. Isomerization allows two strands not initially cleaved to be cut (previous steps repeated) followed by rejoining: the only difference with ser is that all 4 cuts happened simultaneously.
