76
Aging and Sex, DNA Repair in
the gaps and ligase IV and XRCC4 com-
plete the NHEJ repair of the double-strand
break in a chromosome.
As indicated in Table 3, three genes that
act directly in NHEJ [
Ku80
(also called
Ku86
),
WRN
and
BLM
], when defective,
cause early aging.
Ku80
is only active in
NHEJ, while
WRN
and
BLM
also have
roles in HRR.
2.5
MGMT (O
6
-Methylguanine-DNA
Methyltransferase)
As indicated in Table 1, O
6
-methylguanine
is a frequent DNA damage. O
6
-methyl-
guanine is speciFcally repaired by a DNA
repair enzyme called
O
6
-
methylguanine-
DNA
methyltransferase
(MGMT).
As
DNA-PK
cs
DNA-PK
cs
Ku70
Ku86
Ku70
Ku86
Attachment of Ku to DNA ends
and then recruitment of DNA-PKcs
Ku70
Ku86
Ku70
Ku86
WRN
WRN
WRN displaces DNA-PKcs
WRN exonuclease trims ends
Ku70
Ku86
Mre11
Rad50
NBS1
BLM
Alignment of two nearby ends
with pairing at microhomology
Ku70
Ku86
Pol
m
ligase IV
XRCC4
DNA synthesis across gaps
ligation of strand ends
Completion of
Nonhomologous end joining (NHEJ)
BRCA1
Fig. 4
Nonhomologous end joining (NHEJ).
previous page 76 Encyclopedia of Molecular Cell Biology and Molecular Medicine read online next page 78 Encyclopedia of Molecular Cell Biology and Molecular Medicine read online Home Toggle text on/off