Homology-directed DSB repair + homologous recombination

Question 1

Presynapsis (Homology direct repair)

Answer 1

generation of ssDNA at the site of DSB

Question 2

Synapsis (Homology direct repair)

Answer 2

pairing by one of the single stranded ends invading an intact homologous duplex to form a heteroduplex

Question 3

Postsynapsis (Homology direct repair)

Answer 3

repair of the damaged duplex by DNA synthesis using strand from intact duplex as template + separation of the two duplexes

Question 4

Chi

Answer 4

over-represented 8bp sequence that occurs once every 5kbp

Question 5

Which proteins catalyse strand exchange after homologues paring is established?

Answer 5

recombinases

Question 6

Gene conversion

Answer 6

when a break is repaired from a homologues chromosome, the repair has the sequence of the homage now the original sequence

Question 7

Holiday junctions

Answer 7

four arm cross-stranded structures where DNA mols are physically linked by a region of heteroduplex DNA and exchanged strands

Question 8

RuvB

Answer 8

hexametric helicase that moves the holiday junctions along the DNA
BACTERIA

Question 9

RuvAB

Answer 9

the bound to a holiday junction, they unfold into a planar, cross-like structure
~ also recruits RuvC
BACTERIA

Question 10

RuvC

Answer 10

cleaves holiday junction, separating the molecules

BACTERIA

Question 11

Homology-direct DSB repair can use which DNA sources as a template?

Answer 11

~ homologous DNA from:

1) sister chromatid (S/G2)
2) homologous chromosome (G1) - template not exact

Question 12

RecBCD

Answer 12

binds to double strand break, moves along DNA unwinding and degrading it until it comes across a chi sequence
BACTERIA

Question 13

RecA

Answer 13

~ stand exchange recombinase
~ loaded onto ssDNA, forms a presynaptic filament and promotes pairing with homologous DNA
eukaryotic equivalent = Rad51

Question 14

SDSA means

Answer 14

synthesis-dependent strand annealing

Question 15

When is homologous recombination used?

Answer 15

~ crossing over of chromosomes in meiosis
~ bacterial conjugation, transduction and transformation
~ occasionally in mitosis

Question 16

What is the end result of homology-directed repair?

Answer 16

homology-directed repair results in gene conversion

Question 17

What is the end result of homologous recombination?

Answer 17

homologous recombination results in reciprocal exchange of large segments of DNA between homologous duplexes

Question 18

How do homology-directed repair AND homologous recombination differentiating in their processing of one DSB ends?

Answer 18

HR = the 2nd DSB end captures the displaced strand of the D-loop = linked
HDR = the two duplex are not linked

Question 19

Result of 2 HR Holliday Junctions…

Answer 19

~ if both resolved in the same direction = no recombination

~ if resolved in different direction = recombination

Question 20

Spo11

Answer 20

introduces a DSB to initiate meiotic recombination

Question 21

BRAC1 and BRAC2

Answer 21

~ accessory proteins in homology-directed repair of DSB

~ defects common in cancer patients

Question 22

RuvA

Answer 22

forms a tetramer and binds to Holliday junction’s four arms creating a square planar configuration