3,N4-ethenoC (εC) in ssDNA

FULL NAME: 3,N4-ethenocytosine in ssDNA


DESCRIPTION:
3,N4-ethenocytosine (epsilonC) is a highly mutagenic DNA lesion induced by oxidative stress as well as by exposure to industrial chemicals such as vinyl chloride. In normal cells, survival of transfected M13 single-stranded DNA bearing a single epsilonC residue (epsilonC-ssDNA) is about 20% of that of control DNA, with about 5% of the progeny phage bearing a mutation at the lesion site. Most mutations are C → A and C → T, with a slight predominance of transversions over transitions. In contrast, in cells expressing elevated levels of DNA PolII, survival of var epsilonC-ssDNA is close to 100%, with a concomitant mutation frequency of almost 99% suggesting highly efficient translesion DNA synthesis (TLS). Furthermore, an overwhelming majority of mutations at var epsilonC are C → T transitions. Purified DNA PolII efficiently catalyzes translesion synthesis at var epsilonC in vitro, accompanied by high levels of mutagenesis with the same specificity. These results suggest that the observed in vivo effects inDNA PolII over-expressing cells are due to DNA PolII-mediated DNA synthesis. Introduction of mutations in the carboxy terminus region (β interaction domain) of polB gene eliminates in vivo translesion synthesis at var epsilonC, suggesting that the ability of DNA PolII to compete with DNA PolIII requires interaction with the β processivity subunit of PolIII. Thus, PolII can compete with PolIII for translesion synthesis. 3,N4-ethenocytosine (eC) is produced from the same precursors and by the same pathways that generate eA in DNA. As with eA, the BER pathway ([human thymine-DNA-glycosylase (hTDG)] in human and [double-stranded uracil-DNA-glycosylase (dsUDG)] in E.coli) is an established strategy used by nature to suppress the biological effects of this adduct. The cellular defense network against eC additionally involves the AlkB pathway, at least in E.coli, which should be mechanistically similar to that of eA repair by AlkB. In E.coli, AlkB has a modest effect on eC toxicity but reduces the mutation rate of the adduct by about two-thirds from 82% in AlkB-deficient cells to 37% in AlkB-proficient hosts, implying incomplete conversion to cytosine prior to polymerase traversal. The mutations of eC in AlkB-deficient and -proficient cells are C → A and C → T, which are of approximately equal abundance in each cellular background.

DAMAGE TYPE: DNA adduct


DNA DAMAGE SOURCE(S) (MAIN):
reactive oxygen species (ROS)
vinyl chloride metabolites
chloroacetaldehyde (CAA)


DNA DAMAGE EFFECT(S) (MAIN):
C→A transversion
mutagenesis
point mutation
substitution
transversion


DNA DAMAGE EFFECT(S) (MINOR):
C→T transition
mutagenesis
point mutation
substitution
transition


PATHWAYS:
direct reversal (DR)


DNA repair protein(s) related to damage:
ALKBH2


Last modification date: Sept. 2, 2011