Repair of the mutagenic DNA oxidation product, 5-formyluracil

Opposite-base dependent excision of 5-formyluracil from DNA by hSMUG1

“…In addition, the hNTH1 protein investigated by the former study was truncated by lacking 22 residues at the N-terminus, exhibiting a much higher activity than full-length hNTH1. Using HeLa nuclear extract, excision of fU opposite G in DNA was observed to be 10 times more efficient than opposite A (Liu et al 2003). This can, at least in part, be explained by the different kinetics of excision of fU paired with G compared to A shown by hSMUG1 (Table I).…”

“…This also conforms to the observed preference of SMUG1 for uracil opposite G rather than opposite A (Kavli et al 2002) which has been suggested to be inflicted by a wedge motif in hSMUG1 that makes specific contacts with guanine opposite the lesion (Pettersen et al 2007), although from our homology modelling and visualization of the crystal structure of xSMUG1 in complex with double-stranded DNA, no such sequence-specific contacts closer than about 9.5Å can be observed between residues in the wedge-motif of the protein and guanine opposite the lesion. In addition, mammalian TDG and MBD4 proteins may contribute to the excision of fU from DNA when opposite G but exhibit very low or no activity, respectively, when opposite A (Liu et al 2003). hNEIL1 as opposed to hNEIL2 also exhibits some activity for fU in DNA (Katafuchi et al 2004, Zhang et al 2005 (Table II).…”

“…The principal fU glycosylase activity was first characterized in Escherichia coli (Bjelland et al 1994), and a decade later identified in mammalian cells as a function of the SMUG1 (single-strandselective monofunctional uracil-DNA glycosylase 1) protein . In addition, human NTH1 (endonuclease III homologue 1) and MBD4 (methylated DNA-binding domain protein 4) and mouse Tdg (mismatchspecific thymine-DNA glycosylase) proteins, as well as the human nucleotide excision repair complex, have been found to exhibit activity for fU in DNA in vitro (Miyabe et al 2002, Liu et al 2003, Kino et al 2004). …”

A human cancer-associated truncation of MBD4 causes dominant negative impairment of DNA repair in colon cancer cells

“…This was demonstrated by the behaviour of recombinant protein in cell-free gel-shift and glycosylase systems. Some other base-pair mismatches affecting CpG dinucleotides were also shown to be lower affinity substrates for MBD4 activity (Petronzelli et al, 2000a, b) and as time has progressed more substrates have been documented, at least in vitro (Liu et al, 2002;Yoon et al, 2003). The role of MBD4 as a methyl-CpG-focused DNA mismatch glycosylase was subsequently supported by increases in mutation frequency at CpG sites in mouse models lacking Mbd4 (Millar et al, 2002;Wong et al, 2002).…”

“…The first report of substrates of MBD4 showed preference for T Á G products of methyl-C deamination within methyl-CpG sites . Later reports demonstrated a larger set of in vitro CpG mismatches for MBD4 recognition, such as U Á G (Petronzelli et al, 2000a, b), 5-fluorouracil (5-FU) Á G (Petronzelli et al, 2000b), ethenecytosine (eC) Á G (Petronzelli et al, 2000a), 5-formyluracil (5-FoU) Á G (Liu et al, 2002), T Á O 6 -methyl-guanine (O 6 -meG) (Cortellino et al, 2003) and thymine glycol (Tg) Á G (Yoon et al, 2003). Total absence of MBD4 in mice caused an increase in MF especially at CpG sites (Millar et al, 2002;Wong et al, 2002).…”