Chiolo Lecture 9 Flashcards
How can DSBs be studied?
by imaging repair foci (=’sites’) in cells exposed to ionizing radiation (IR)
What experiments allow to identify proteins required for DSB repair?
RNAi experiments
What is the mobility of chromosomes without DSBs?
limited mobility
How are DSB repair imaged in live imaging?
repair proteins are fused with a fluorescent tag (GFP, YFP, mCherry)
What is the mobility of chromosomes with DSBs?
explore more space in the nucleus
What does increased mobility of chromosomes facilitate?
homology search
What is pericentromeric heterochromatin mostly composed of?
- repeated sequences (30% of fly/ human genomes)
- mostly composed of DNA repeats = transposons and ‘satellite sequences’
Why are pericentromeric heterochromatin composed of DNA repeats?
required for centromere stability
What are repeated sequences used as?
repeated sequences on different chromosomes can be used as templates for repair leading to ‘aberrant recombination’
What prevents chromosome rearrangements?
specialized mechanisms that regulate repair in repeated sequences, these mechanisms rely on nuclear dynamics
What does aberrant recombination result in?
translocations in cancer cells
What forms a distinct ‘domain’
Drosophila heterochromatin
What is discovery 1?
DSBs leave the heterochromatin domain
What is the discovery 2?
HR repair continues at nuclear periphery
Why do heterochromatic DSBs move to the nuclear periphery?
to prevent aberrant recombination
What does prevention of aberrant recombination allow?
‘strand invasion’ to occur away from other repeated nuclear sequences
What is the movement of sister chromatids?
move together with the DSB
What is discovery 3?
nuclear actin filaments drive relocalization
What does defective movement result in?
defective repair and massive chromosome rearrangements
Where does relocalization of DSBs occur?
repeated DNA sequences
What does relocalization isolate?
repair sites from similar sequences on other chromosomes to prevent aberrant recombination
What is the function of recombinases?
cleaves and rejoin DNA molecules to invert, duplicate, relocalize, and delete portions of the genome
How does recombinases cleave and rejoin DNA?
- serine (or tyrosine) breaks a phosphodiester bond
- formation of high energy bond with phosphate
- phosphodiester bond with new DNA
