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in transcription-coupled repair. The proposed TC-NER model in animal cells is es-
sentially derived from the finding that TFIIS is able to assist RNAPII to bypass tran-
scription arrest sites (Gnatt
2002
). However, a recent study carried out by MacK-
innon-Roy et al. (
2011
) has demonstrated that the TFIIS function is not a limiting
factor for TC-NER since RNA interference directed against TFIIS did not affect the
sensitivity of human cell to oxidative stress. In a different report (Jensen and Mul-
lenders
2010
), downregulation of human TFIIS by RNA interference significantly
delays, but does not suppress, the recovery of UV-inhibited transcription. According
to these authors, downregulation of TFIIS causes an increased level of hyperphos-
phorylated RNAPII, which in turn needs to be degraded.
In plants, there are only a few reports dealing with the TFIIS function (Grasser
et al.
2009
; Macovei et al.
2011
; Balestrazzi et al.
2011c
) and the presence of a
TFI-
IS-like
gene encoding a TFIIS-related protein has been described (Macovei et al.
2011
). The
TFIIS-like
gene encodes a product with unknown function, conserved
among plant species, and shares some structural features with the canonical TFIIS
protein, elongin A (Transcription Elongation Factor SIII), and CRSP70 (Cofactor
Required for Sp1 activation). The expression profiles of the
TFIIS
and
TFIIS
-like
genes were analyzed in barrel medic plantlets exposed to heavy metal and osmotic
stress, respectively. Both genes were significantly up-regulated in aerial parts and
roots of plants exposed to toxic copper doses as well as in plants grown in the pres-
ence of polyethylene glycol (PEG) as osmotic agent (Macovei et al.
2011
).
6 Expression Profiles of Base Excision Repair Genes
in Response to Abiotic Stresses
Oxidative DNA damage is associated with the accumulation of the oxidized base
7,8-dihydro-8-oxoguanine (8-oxo-dG), which is highly mutagenic since it frequent-
ly mispairs with the incoming dAMP during DNA replication, causing G:C to T:A
transversions. Oxidized bases are usually removed through the BER pathway, initi-
ated by DNA glycosylases that hydrolytically cleave the glycosylic bond between
the target base and deoxyribose, releasing the damaged base and leaving an AP site
that are further processed (Roldan-Arjona and Ariza
2009
).
Poly(ADP-Ribose)Polymerase 1 (PARP-1), a nuclear protein which interacts
with factors involved in the modulation of chromatin architecture and cell recovery
from DNA damage, is among the BER components responsive to stresses (Douchet-
Chablaud et al.
2001
). Both the
Arabidopsis
PARP
genes
AtPARP1
and
AtPARP2
are stress responsive and the preferential accumulation of the
AtPARP2
transcript in
response to heavy metal stress suggests for specific roles played in plants by each
gene (Douchet-Chablaud et al.
2001
).
In plants, 8-oxoguanine DNA glycosylase/lyase (OGG1) and formamidopyrim-
idine-DNA glycosylase (FPG) play similar roles within the BER pathway involved
in the removal of oxidized bases, e.g., 8-oxo-dG and formamidopyrimidine (FAPy)
lesions. Macovei et al. (
2011b
) have investigated the possible roles played in plants
