Xeroderma pigmentosum (XP)  is a human autosomal recessive disease,
characterized by a high incidence of sunlight-induced skin cancer. People's
skin cells with this condition are hypersensitive to ultraviolet light, due
to defects in the incision step of DNA excision repair. There are a minimum of
seven genetic complementation groups involved in this pathway: XP-A to XP-G.
The defect in XP-G can be corrected by a 133 Kd nuclear protein called XPG (or
XPG belongs to a family of proteins [2,3,4,5,6] that are composed of two
Subset 1, to which belongs XPG, RAD2 from budding yeast and rad13 from
fission yeast. RAD2 and XPG are single-stranded DNA endonucleases [7,8].
XPG makes the 3'incision in human DNA nucleotide excision repair .
Subset 2, to which belongs mouse and human FEN-1, rad2 from fission yeast,
and RAD27 from budding yeast. FEN-1 is a structure-specific endonuclease.
In addition to the proteins listed in the above groups, this family also
Fission yeast exo1, a 5'->3' double-stranded DNA exonuclease that could act
in a pathway that corrects mismatched base pairs.
Yeast EXO1 (DHS1), a protein with probably the same function as exo1.
Sequence alignment of this family of proteins reveals that similarities are
largely confined to two regions. The first is located at the N-terminal
extremity (N-region) and corresponds to the first 95 to 105 amino acids. The
second region is internal (I-region) and found towards the C-terminus; it
spans about 140 residues and contains a highly conserved core of 27 amino
acids that includes a conserved pentapeptide (E-A-[DE]-A-[QS]). It is possible
that the conserved acidic residues are involved in the catalytic mechanism of
DNA excision repair in XPG. The amino acids linking the N- and I-regions are
not conserved; indeed, they are largely absent from proteins belonging to the
We have developed two signature patterns for these proteins. The first
corresponds to the central part of the N-region, the second to part of the I-region and includes the putative catalytic core pentapeptide.
O'Donovan A., Scherly D., Clarkson S.G., Wood R.D.
J. Biol. Chem. 269:15965-15968(1994).
O'Donovan A., Davies A.A., Moggs J.G., West S.C., Wood R.D.
PROSITE is copyright. It is produced by the SIB Swiss Institute
Bioinformatics. There are no restrictions on its use by non-profit
institutions as long as its content is in no way modified. Usage by and
for commercial entities requires a license agreement. For information
about the licensing scheme send an email to
or see: prosite_license.html.