Methyl- and Normal-Cytosine Deamination by the Foreign DNA Restriction Enzyme APOBEC3A

UMMS Affiliation

Department of Biochemistry and Molecular Pharmacology

Publication Date


Document Type



Proteins; Cytidine Deaminase; DNA Restriction Enzymes; 5-Methylcytosine


Biochemistry, Biophysics, and Structural Biology | Pharmacology, Toxicology and Environmental Health


Multiple studies have indicated that the TET oxidases and, more controversially, the AID/APOBEC deaminases have the capacity to convert genomic DNA 5-methylcytosine (MeC) into altered nucleobases that provoke excision repair and culminate in the replacement of the original MeC with a normal cytosine (C). We show that human APOBEC3A (A3A) efficiently deaminates both MeC to thymine (T) and normal C to uracil (U) in single-stranded DNA substrates. In comparison, the related enzyme APOBEC3G (A3G) has undetectable MeC-to-T activity and 10-fold less C-to-U activity. Upon 100-fold induction of endogenous A3A by interferon, the MeC status of bulk chromosomal DNA is unaltered whereas both MeC and C nucleobases in transfected plasmid DNA substrates are highly susceptible to editing. Knockdown experiments show that endogenous A3A is the source of both of these cellular DNA deaminase activities. This is the first evidence for non-chromosomal DNA MeC-to-T editing in human cells. These biochemical and cellular data combine to suggest a model in which the expanded substrate versatility of A3A may be an evolutionary adaptation that occurred to fortify its innate immune function in foreign DNA clearance by myeloid lineage cell types.

DOI of Published Version



J Biol Chem. 2012 Oct 5;287(41):34801-8. doi: 10.1074/jbc.M112.385161. Epub 2012 Aug 15. Link to article on publisher's site

Journal/Book/Conference Title

The Journal of biological chemistry

Related Resources

Link to Article in PubMed

PubMed ID