DNMT1 is the principal mammalian DNA methyltransferase responsible for maintaining DNA methylation patterns established during development 1. It preferentially methylates hemimethylated CpG residues and associates with DNA replication sites during S phase to preserve epigenetic inheritance 234. Beyond its canonical DNA methylation function, DNMT1 exhibits a dual role by binding mRNA transcripts and facilitating 5-methylcytosine RNA methylation through NSUN2 recruitment, thereby regulating genes involved in mitochondrial function 5. DNMT1 mediates transcriptional repression through direct HDAC2 binding and associates with tumor suppressor gene promoters, contributing to their silencing in cancer cells 67. During erythropoiesis, DNMT1 exerts stage-specific functions: it maintains p21 promoter methylation to regulate cell cycle progression in progenitors and maintains protein homeostasis during terminal differentiation by controlling RPL15-mediated endoplasmic reticulum stress 8. DNMT1 also regulates viral replication through DNA methylation of viral genomes, with human bocavirus NS1 protein promoting DNMT1 degradation to enhance viral RNA processing 9. Mutations in DNMT1's replication focus targeting sequence domain cause autosomal dominant cerebellar ataxia-deafness and narcolepsy through aberrant RNA methylation and mitochondrial dysfunction 5. RAD51 safeguards DNMT1 stability and function by inhibiting UHRF1-mediated degradation and facilitating DNMT1 recruitment to chr19 10.