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Updated: Aug 7, 2026
Uracil-DNA Glycosylase Assay by Matrix-assisted Laser Desorption/Ionization Time-of-flight Mass Spectrometry Analysis
Published on: April 22, 2022
Genomic uracil and human disease
Lars Hagen1, Javier Peña-Diaz, Bodil Kavli
1Department of Cancer Research and Molecular Medicine, Faculty of Medicine, Norwegian University of Science and Technology, Trondheim.
Abstract:
Uracil is present in small amounts in DNA due to spontaneous deamination of cytosine and incorporation of dUMP during replication. While deamination generates mutagenic U:G mismatches, incorporated dUMP results in U:A pairs that are not directly mutagenic, but may be cytotoxic. In most cells, mutations resulting from uracil in DNA are prevented by error-free base excision repair. However, in B-cells uracil in DNA is also a physiological intermediate in acquired immunity. Here, activation-induced cytosine deaminase (AID) introduces template uracils that give GC to AT transition mutations in the Ig locus after replication. When uracil-DNA glycosylase (UNG2) removes uracil, error-prone translesion synthesis over the abasic site causes other mutations in the Ig locus. Together, these processes are central to somatic hypermutation (SHM) that increases immunoglobulin diversity. AID and UNG2 are also essential for generation of strand breaks that initiate class switch recombination (CSR). Patients lacking UNG2 display a hyper-IgM syndrome with recurrent infections, increased IgM, strongly decreased IgG, IgA and IgE and skewed SHM. UNG2 is also involved in innate immune response against retroviral infections. Ung(-/-) mice have a similar phenotype and develop B-cell lymphomas late in life. However, there is no evidence indicating that UNG deficiency causes lymphomas in humans.
Insights
Uracil in DNA, usually repaired, is vital for B-cell immunity via activation-induced cytosine deaminase (AID) and uracil-DNA glycosylase (UNG2). UNG2 deficiency impairs immune responses and immunoglobulin diversification.
Area of Science:
- Immunology
- Molecular Biology
- Genetics
Background:
- Uracil occurs in DNA from cytosine deamination or dUMP incorporation.
- While typically repaired, uracil in DNA plays a crucial role in B-cell adaptive immunity.
- Activation-induced cytosine deaminase (AID) and uracil-DNA glycosylase (UNG2) are key enzymes involved.
Purpose of the Study:
- To elucidate the dual role of uracil in DNA: as a potential mutagen and a physiological intermediate in B-cell immunity.
- To understand the mechanisms of somatic hypermutation (SHM) and class switch recombination (CSR) involving uracil.
- To investigate the consequences of uracil-DNA glycosylase (UNG2) deficiency in immune function and disease susceptibility.
Main Methods:
- Analysis of DNA repair pathways involving uracil.
- Investigating the function of activation-induced cytosine deaminase (AID) and uracil-DNA glycosylase (UNG2) in B-cells.
- Studying phenotypes of patients and mice lacking functional UNG2.
Main Results:
- Uracil in DNA is managed by base excision repair, but also utilized by AID and UNG2 in immunoglobulin loci for SHM and CSR.
- UNG2 deficiency leads to impaired immunoglobulin diversification, a hyper-IgM syndrome, and increased susceptibility to infections.
- While Ung(-/-) mice develop B-cell lymphomas, human UNG2 deficiency is not linked to lymphoma development.
Conclusions:
- Uracil processing by UNG2 is essential for adaptive immunity, specifically for generating antibody diversity and class switching.
- UNG2 plays a critical role in both innate and adaptive immune responses.
- The distinct outcomes of UNG2 deficiency in mice and humans warrant further investigation regarding lymphoma risk.
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