Cellular response to DNA Damage and Repair II Flashcards
TLS
Translesion DNA Synthesis; component of SOS response; In play when DNA damage is extensive
Error Prone Repair Def. and Mechanism
1) DNAP III Senses error and halts 2) B-clamp dissociates as well as DNAP III 3) Halting recruits DNAP IV or V (EPP Error prone polymerase) 4) EPP deposits random nucleotides, has no proofreading ability 5) Other Repair mechanisms hopefully will fix damage.
When is NHEJ likely to occur?
Mostly during G1, when a sister chromatid is absent
When is HEJ likely to occur?
Most likely after S phase when a sister chromatid is available.
SOS response in bacteria
1) RecA is normally low 2) Stalling of DNA replication initiates the binding of RecA to ssDNA 3) RecA activated and cleaves LexA 4) cleavge of LexA repressor leads to its inactivation (via activated self proteolysis) 5) Leads to the production of many SOS genes. 6) Once repairs are made. RecA decreases the binding affinity for ssDNA, leads to LexA increase and inhibition.
RecA roles
1) represses LexA 2) leads ssDNA to sister chromatid 3) Binds to ssDNA, slightly unwinds it, and leads it to homologous chromosome.
RecC
Protein that finds ds breaks and aids in the loading of RecB and RecD (helicases).
RecB
3’ to 5’ helicase activity. Endonuclease activity as well. Produces 3’OH at Chi site
RecD
5’ to 3’ helicase
Chi sequence
5’-GCTGGTGG-3’
RecA primary Binding site
Binds ssDNA
RecA secondary site
Bind dsDNa. Unwinds and checks for homology.
RuvA
maintains holiday junction geometry
RuvB
helicase. Moves junction
RuvC
Endonuclease cuts strands to resolve the junction. Separates the two duplex DNAs.
