Recombinant APOBEC3A (A3A) Protein is a single-domain cytidine deaminase with antiviral properties that deaminates cytidine into uracil, allowing for specific detection of DNA methylation levels. This protein is recombinantly expressed in Escherichia coli and is suitable for bisulfite-free whole-genome sequencing of 5-hydroxymethylcytosine (e.g., ACE-Seq) and cytidine deamination.