Aborted/incomplete DSBR

Question 1

What happen in single strand annealing (SSA)?

Answer 1

This is a RAD51 independent pathway where after the break 5’ end resection occurs. RPA’s are displaced to reveal homologous sequences. Strand annealing occurs between the two complementary overhangs and the ends are joined.

Question 2

What is the disadvantage with SSA?

Answer 2

There is the possibility that the middle portion of genetic information will be lost.

Question 3

What happens in Microhomology-Mediated End Joining (MMEJ)?

Answer 3

This NHEJ without the use of classical NHEL factors.

1. After resection, DNA Polymerase ⍬ displaces RPA with its helicase activity to reveal microhomology between strands.
2. DNA Pol ⍬ polymerase activity stabilises the the complementary pairing between the two ends.
3. Other DNA polymerases may be needed to complete synthesis.
4. Flap are trimmed and nick are ligated.

Question 4

What happens in Microhomology -Mediated Template Switching?