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| • |
XP-A
participates in photoproduct recognition and DNA
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binding
This binding may be followed by the formation of a
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quasi-stable
complex consisting of XPA, XPC, human single-
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strand
binding protein (RPA/HSSB), and TFIIH, which then
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acts
as a nucleation site for binding of the incision/excision
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enzymes.
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| • |
XP-B is
a 3’-> 5’ DNA helicase that may be involved in
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unwinding
the DNA 5'-ward of a damaged base
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XP-C is
a single-stranded DNA binding protein that is
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essential
for repair of the nontranscribed regions of the
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genome,
that acts in the initial step of damage recognition.
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XP-D
is a 5'–3' helicase, a component of transcription factor
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TFIIH
may be involved in 3'-ward unwinding of the DNA in
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the
vicinity of a damaged base
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