recombinational repair in bacteria
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- what kind of enzyme?
- what are its functions (2)?
- helicase & nuclease - unwinds & degrades
- 1. degrades 5' at DSB
- -binds at free 5' & moves inward on the helix unwinding & degrading; coupled to ATP hydrolysis
- 2. loads RecA onto ss-tail
RecBCD component functions...
- -helicase motors (B-moves 3'->5' on 1 strand & nuclease & loads RecA, D-moves 5'->3' on other)
- - RecC binds chi on the 3' alters RecB degradation (stops on 3' & increases on 5')
- -5'-GCTGGTGG-3' sequence on the 3'end at DSB
- -binds RecC
- -initiates 5' degradation = ss 3' tail
SSB at 3'-ss tail
ssDNA binding proteins block RecA etc.
gap filling bacteria polymerase
helicase at stalled replication fork promotes regression
- -recombinase, loaded & nucleated by RecB of RecBCD complex facilitating strand invasion
- - also must be loaded onto ssDNA gaps- DNA-dependent ATPase, filament nucleoprotein causes extension of nucleated filament in 5'->3'
- - align a ssDNA with homologous dsDNA & switching => strand invasion
- -highly regulated
loads RecA on ssDNA gaps
- RecF of RecFOR
- collectively activate & load RecA
RecA regulation, 3 levels:
- regulation by other proteins
when does homologous recombination occur during meiosis?
metaphase, meiosis I
fork collapse repair mechanism
- 1. RecBCD - 5' nuclease activity at break; recruitment of RecA
- 2. RecA strand invasion (intact dsDNA seperates & aligns with 3' ss-tail)
- 3. RuvAB branch migration (intact dsDNA continues to seperate & digested 5' aligns with other intact strand)
- 4. RuvC & ligase cleavage at (3'->5' strand Y-cross) = Holliday intermediate resolution then ligation
- RuvA tetramer - binds DNA Holliday intermediate
- RuvB - DNA translocase, coupled to ATP hydrolysis
- RuvAB - & promotes branch migration
- RuvC - resolvase
what restarts replication?
restart primosome complex loads replicative helicase DnaB onto DNA => rep. fork
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