Properties and functions of human uracil-DNA glycosylase from the UNG gene.
The human UNG-gene at position 12q24.1 encodes nuclear (UNG2) and mitochondrial (UNG1) forms of uracil-DNA glycosylase using differentially regulated promoters, PA and PB, and alternative splicing to produce two proteins with unique N-terminal sorting sequences. PCNA and RPA co-localize with UNG2 in replication foci and interact with N-terminal sequences in UNG2. Mitochondrial UNG1 is processed to shorter forms by mitochondrial processing peptidase (MPP) and an unidentified mitochondrial protease. The common core catalytic domain in UNG1 and UNG2 contains a conserved DNA binding groove and a tight-fitting uracil-binding pocket that binds uracil only when the uracil-containing nucleotide is flipped out. Certain single amino acid substitutions in the active site of the enzyme generate DNA glycosylases that remove either thymine or cytosine. These enzymes induce cytotoxic and mutagenic abasic (AP) sites in the E. coli chromosome and were used to examine biological consequences of AP sites. It has been assumed that a major role of the UNG gene product(s) is to repair mutagenic U:G mispairs caused by cytosine deamination. However, one major role of UNG2 is to remove misincorporated dUMP residues. Thus, knockout mice deficient in Ung activity (Ung-/- mice) have only small increases in GC-->AT transition mutations, but Ung-/- cells are deficient in removal of misincorporated dUMP and accumulate approximately 2000 uracil residues per cell. We propose that BER is important both in the prevention of cancer and for preserving the integrity of germ cell DNA during evolution.
Krokan
H E
HE
Institute of Cancer Research and Molecular Biology, Norwegian University of Science and Technology, N-7489 Trondheim, Norway.
Otterlei
M
M
Nilsen
H
H
Kavli
B
B
Skorpen
F
F
Andersen
S
S
Skjelbred
C
C
Akbari
M
M
Aas
P A
PA
Slupphaug
G
G
D000818:Animals; D001080:Apurinic Acid / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology; D001665:Binding Sites; D020134:Catalytic Domain; D002453:Cell Cycle; D002874:Chromosome Mapping; D002881:Chromosomes, Human, Pair 12 / Q000235:genetics; D045647:DNA Glycosylases; D004260:DNA Repair; D004272:DNA, Mitochondrial / Q000235:genetics / Q000378:metabolism; D043224:Deoxyribonuclease (Pyrimidine Dimer); D003856:Deoxyuracil Nucleotides / Q000378:metabolism; D004706:Endodeoxyribonucleases / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D015971:Gene Expression Regulation, Enzymologic; D005796:Genes; D006801:Humans; D051379:Mice; D018345:Mice, Knockout; D008928:Mitochondria / Q000201:enzymology; D005810:Multigene Family; D009699:N-Glycosyl Hydrolases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D010766:Phosphorylation; D011401:Promoter Regions, Genetic; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D011743:Pyrimidines / Q000378:metabolism; D013941:Thymine / Q000031:analogs & derivatives* / Q000378:metabolism; D051981:Uracil-DNA Glycosidase
D001426:Bacterial Proteins; D004272:DNA, Mitochondrial; D003856:Deoxyuracil Nucleotides; D011743:Pyrimidines; D001080:Apurinic Acid; C029389:thymine glycol; C007267:2'-deoxyuridylic acid; D004706:Endodeoxyribonucleases; D043224:Deoxyribonuclease (Pyrimidine Dimer); D045647:DNA Glycosylases; D009699:N-Glycosyl Hydrolases; D051981:Uracil-DNA Glycosidase; D013941:Thymine