Disease relevance of NTG1

• Saccharomyces cerevisiae possesses two Escherichia coli endonuclease III homologs, NTG1 and NTG2, whose gene products function in the base excision repair pathway and initiate removal of a variety of oxidized pyrimidines from DNA [1].

High impact information on NTG1

• Replacement of the signal recognition particle (SRP) 7S gene (SCR1) on a replicating plasmid with scr1-1 (G to A at 129 and A to T at 131 in the consensus sequence -GNAR- in the loop of domain III) resulted in temperature sensitivity for growth of cells in which both chromosomal SRP 7S RNA genes were deleted [2].
• Targeted gene disruption of NTG1 produces a mutant that is sensitive to H2O2 and menadione, indicating that NTG1 is required for repair of oxidative DNA damage in vivo [3].
• S. cerevisiae NTG1 does not have the [4Fe-4S] cluster DNA binding domain characteristic of the other members of this family [3].
• When expressed in E. coli, the NTG1 gene product cleaves plasmid DNA damaged by osmium tetroxide, thus, indicating specificity for thymine glycols in DNA similarly as is the case for EndoIII [3].
• Purified Ntg1, a base excision repair enzyme, introduced a double-stranded break by itself into HS [ori5] [rho(-)] mtDNA at ori5 isolated from yeast cells [4].

Biological context of NTG1

• Substrate specificities of the ntg1 and ntg2 proteins of Saccharomyces cerevisiae for oxidized DNA bases are not identical [5].
• We conclude that functions of both NTG1 and NTG2 are important for removal of oxidative DNA damage in yeast [6].
• However, ntg1 null strains did not exhibit a mitochondrial respiration-deficient (petite) phenotype, suggesting that mtDNA damage is negotiated by the cooperative actions of multiple damage resistance pathways [7].
• Null mutations in ABF2 or PIF1, two genes implicated in mtDNA maintenance and recombination, exhibit a synthetic-petite phenotype in combination with ntg1 null mutations that is accompanied by enhanced mtDNA point mutagenesis in the corresponding double-mutant strains [7].
• These biochemical studies strongly support an important biological role for Ntg1p and Ntg2p in the initial processing of abasic sites and maintenance of genomic stability [1].

Anatomical context of NTG1

• Ntg2 appears to be a nuclear enzyme, whereas Ntg1 was sorted both to the nucleus and to the mitochondria [6].
• It is proposed that the ribosomes of yeast cells expressing SCR1 undergo a conformational change during their interaction with the ER, which lowers their affinity for cyh-binding [8].
• In contrast, a beta-galacosidase-tagged SCR1 was found to be integrated in the endoplasmic reticulum (ER) [8].

Associations of NTG1 with chemical compounds

• Moreover, the Ntg1 protein releases free 8-OH-Gua from 8-OH-Gua/Gua duplex but not from duplexes containing 8-OH-Gua mispaired with adenine, thymine or cytosine [5].
• The results show that the Ntg1 protein preferentially cleaves a DNA duplex containing 8-OH-Gua mispaired with a guanine [5].
• The Ntg1 and Ntg2 proteins also release 2, 6-diamino-4-hydroxy-5-N-methylformamido-pyrimidine from damaged poly(dG-dC).poly(dG-dC) [5].
• In contrast, Ntg1 and Ntg2 proteins do not release 8-hydroxyguanine or 8-hydroxyadenine from gamma-irradiated DNA [5].
• Saccharomyces cerevisiae Endo III homologs (NTG1 and NTG2) have been shown to recognize formamidopyrimidine (Fapy) lesions that are derived from purine [9].

Other interactions of NTG1

• The Ntg1 and Ntg2 proteins were overexpressed in E.coli and purified to apparent homogeneity [5].
• The hyper-rec and mutator phenotypes of the ntg1 ntg2 apn1 triple mutant are further enhanced by the elimination of the nucleotide excision repair pathway [10].
• The additional disruption of the RAD52 gene in the ntg1 ntg2 apn1 triple mutant confers a high degree of sensitivity to these agents [10].
• In yeast mitochondria, three N-glycosylases have been identified so far, Ntg1p, Ogg1p and Ung1p [11].
• Genetic analyses revealed that the combined inactivation of OGG1 and OGG2 [encoding an isoform of the Ogg1 protein, also known as endonuclease three-like glycosylase I (Ntg1)] leads to suppression of spontaneously arising mutations in the mitochondrial genome when compared with the ogg1 single mutant or the wild-type [12].

Analytical, diagnostic and therapeutic context of NTG1

• The substrate specificity of Ntg1 and Ntg2 proteins for modified bases in oxidatively damaged DNA was investigated using gas chromatography/isotope-dilution mass spectrometry [5].
• Northern blot and promoter fusion analysis showed that NTG1 is inducible by cell exposure to DNA-damaging agents, whereas NTG2 is constitutively expressed [6].
• Hemagglutination-inhibition tests with domain-deleted srDAF showed that UMC is on SCR-4 and confirmed that Tca, TcaTcb, and WESb are on SCR-1; Dra is on SCR-3; and Cra is on SCR-4 [13].
• In addition, chromatin immunoprecipitation assays revealed a switching of Scr1 to Rst2 bound at UAS2 during glucose derepression [14].

References