Opposite-base dependent excision of 5-formyluracil from DNA by hSMUG1.
OBJECTIVE
The aim of this study was to determine the excision efficiency of hSMUG1 (human single-strand-selective monofunctional uracil-DNA glycosylase) for 5-formyluracil (fU), a major thymine lesion formed by ionizing radiation, opposite all normal bases in DNA, to possibly explain mutation induction by fU in the DNA of mammalian cells.


METHODS
An enzymatically [(32)P]labelled fU-containing 36 nucleotide DNA sequence plus its complementary sequence (with an A, C, G or T residue inserted opposite fU) was subjected to hSMUG1 in a pH 7.5-buffer, followed by NaOH-mediated cleavage of the resultant abasic sites. Cleaved and uncleaved DNA were separated by denaturing electrophoresis and quantified by autoradiography.


RESULTS
The hSMUG1 excised fU from DNA opposite all normal bases with the highest activity when opposite non-cognate C or T followed by G and cognate A.


CONCLUSIONS
The predominant T --> G and T --> A transversions induced by fU in mammalian cells may be explained by replicative incorporation of C and T, respectively, opposite the lesion and subsequent SMUG1-initiated repair of fU.
Faculty of Science and Technology, Department of Mathematics and Natural Sciences, University of Stavanger, Stavanger, Norway.
Ingeborg
I
Knaevelsrud
Geir
G
Slupphaug
Ingar
I
Leiros
Akira
A
Matsuda
Peter
P
Ruoff
Svein
S
Bjelland
D000818:Animals; D020029:Base Pairing; D001483:Base Sequence; D020134:Catalytic Domain; D004247:DNA / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004260:DNA Repair; D006801:Humans; D007700:Kinetics; D051379:Mice; D008958:Models, Molecular; D009154:Mutation; D051381:Rats; D014498:Uracil / Q000031:analogs & derivatives* / Q000378:metabolism; D051981:Uracil-DNA Glycosidase / Q000737:chemistry / Q000378:metabolism*
C007777:5-formyluracil; D014498:Uracil; D004247:DNA; C498095:SMUG1 protein, human; D051981:Uracil-DNA Glycosidase