This holoenzyme is involved in the editing of cytosine-to-uracil (C-to-U) nucleotide bases in apolipoprotein B and neurofibromin 1 mRNAs.

[6] Its function relies on introducing a stop codon into apolipoprotein B (ApoB) mRNA, which alters lipid metabolism in the gastrointestinal tract.

A1’s deamination of the cytosine base yields uracil, which creates a stop codon in the mRNA.A1 has been linked with both positive and negative health effects.

[12] The editing amount, or expression, of A1 performs is correlated with the insulin concentration in the nucleus, the site of modification.

[13][14] Tests involving A1 mutants with various deleted amino acid sequences have shown that editing activity is dependent on residues 14 to 35.

Like all APOBEC proteins, A1 coordinates a zinc atom with two cysteine and one histidine residues that serve as a Lewis acid.

Its diffusion toward the nucleic membrane can lead it to mutate DNA sequences that are actively transcribed on the genome.

[19] A pan-cancer study shows that A1 mRNA level is associated with adverse prognosis as well as higher rate of the human genomic insertions and deletions (indels), particularly in-frame ones, which proposes its endogenous mutator activity.