APOBEC1 is a cytidine deaminase enzyme that catalyzes the conversion of cytidine to uridine in RNA through post-transcriptional editing 1. Its primary function involves editing specific mRNA transcripts, most notably converting a CAA (glutamine) codon to UAA (stop codon) in apolipoprotein B mRNA, which generates truncated ApoB48 protein essential for lipid metabolism 1. The enzyme also participates in editing other transcripts, contributing to diverse cellular processes. Mechanistically, APOBEC1 functions as part of larger ribonucleoprotein complexes that confer editing specificity and activity 1. The enzyme has been extensively utilized in genome editing applications, where engineered APOBEC1-Cas9 fusion proteins enable precise C-to-T base editing without requiring double-strand DNA breaks 12. Evolved variants like evoAPOBEC1 demonstrate improved editing efficiency across different sequence contexts 2. In disease contexts, APOBEC1 activity has been implicated in cancer mutagenesis, with evidence suggesting APOBEC family enzymes contribute to the characteristic cytidine mutation patterns observed in breast cancers 3. The enzyme's base editing capabilities have proven valuable for both research applications and potential therapeutic genome editing, offering a precise method for correcting point mutations relevant to human diseases 145.