APOBEC1 deaminates cytosine both in RNA and ssDNA and has roles in both mRNA editing and ssDNA mutagenesis as part of the defense against retroviruses and genomic retrotransposons [1].

1: Diversification of AID/APOBEC-like deaminases in metazoa: multiplicity of clades and widespread roles in immunity. Krishnan A, Iyer LM, Holland SJ, Boehm T, Aravind L; Proc Natl Acad Sci U S A. 2018;115:E3201. PMID:29555751