Area of Research: DNA recombination and repair


Cells invest a great deal of energy in minimizing genomic changes. In
addition to the external environmental insults, DNA double strand breaks
are also made and repaired during meiosis when recombination takes
place between paired homologous chromosomes.

Two major repair pathways exist to deal with double strand breaks (dsbs)
in metazoans : Non-homologous end joining (NHEJ) and homologous
recombination (HR) pathways. Our molecular knowledge of the eukaryotic
system of dsb repair dates from the definition of yeast mutants hyper-
sensitive to dsbs induced by ionizing radiation. Since the predominant
system of dsb repair in yeast is HR, the cloning of the responsible genes
revealed the extreme conservation of key elements of the HR apparatus
from bacteria to eukaryotes. The paucity of mammalian HR mutants,
suggests that nonhomologous end-joining may be a major mechanism
of rejoining DNA ends. Our lab is involved in dissecting out events
responsible for interaction and / or competition between NHEJ and
HR pathways in DT40 chicken cells.

H R proteins in vertebrates

Rad51, Rad52, Rad54, RAD54B,
Mre11/Rad50/NBS complex
Brca1, Brca2

Rad51-related proteins

Rad51B, Rad51C, Rad51D

Other proteins

p53, PARP


By using gene targeting strategies we have created mutant DT40 cell
lines, some of which have been listed below. Creation of single and
double mutant cell lines against repair/recombination specific genes
have improved our understanding of the interaction between HR and
NHEJ pathways.

Single mutants

1. ATM -/-
2. BLM Helicase -/-
3. Ku70 -/-
4. Mre11 -/-
5. Rad51 -/-
6. Rad51B -/-
7. Rad51 C-/-
8. Rad51D-/-
9. Rad52 -/-
10. Rad54 -/-
11. XRCC2-/-
12. XRCC3-/-

Double mutants

1. ATM -/- Ku70 -/-
2. BLM Helicase -/- RAD54-/-
3. RAD54-/- ATM-/-
4. Rad54 -/- Ku70 -/-
5. Rad54-/- Rad54B-/-


The field of DNA repair and recombination is a rapidly growing branch of
science that has attracted enormous attention from the scientific community.
Due to new findings arriving faster than expected it is difficult to
predict how this field will appear in a decade from now. The ability to
manipulate homologous recombination would remove a major obstacle to
the targeted delivery of genes. In this direction, we are studying single and
double gene knockout cell lines that show defective repair potential. One of
our important objectives is to understand why DT40 cell lines show high
targeting efficiency? Till now no plausible mechanism has been reported. We
hope to answer this question sooner than later.

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