Aging and Sex, DNA Repair in
71
Apoptosis
DNA with bulky lesion (e.g. UV photoproduct)
XPB
XPD
XPB
XPD
XPB
XPD
XPB
XPD
XPB
XPD
TFIIH
p53
p53
p53
Completion of
nucleotide excision repair (NER)
XPC-hHR23B
or
XPA-RPA
or
XPE(p48)-p125
(UV-DDB)
Recognition of DNA damage
Recruitment of repair complex
Steps involving
helicases
ERCC1
XPF
ERCC1
XPF
ERCC1-XPF
recruitment
Formation of
incision complex
Dual incisions (3' and 5')
and release of segment with damage
Polymerization
Fig. 1
Nucleotide excision repair (NER).
can be initiated by removal of a dam-
aged base by a DNA glycosylase, which
binds the altered deoxynucleoside in an
extrahelical position and catalyzes cleav-
age of the base–sugar bond, or can
occur at a site of spontaneous depurina-
tion [an apurinic (AP) site] (Fig. 2). The
glycosylases that remove damaged bases
are speci±c to the particular damage. Ref-1
(also called apurinic/apyrimidinic endonu-
clease or APE) then makes a 5
0
nick in
the DNA backbone, followed by PARP,
1 acting as a nick surveillance protein.
PARP locates at the site of the single chain
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