The study investigates the role of TET1 in transcription and DNA methylation fidelity. TET1 is found to bind extensively to the genome, particularly at CpG-rich promoters and within genes, where it converts 5-methylcytosine (mC) to 5-hydroxymethylcytosine (hmC). hmC is enriched at transcription start sites (TSSs) and gene bodies, contrasting the distribution of mC. TET1 is also associated with transcriptional repression, binding a significant proportion of Polycomb group target genes and colocalizing with the SIN3A co-repressor complex. The study suggests that TET1 fine-tunes transcription, opposes aberrant DNA methylation at CpG-rich sequences, and contributes to the regulation of DNA methylation fidelity.The study investigates the role of TET1 in transcription and DNA methylation fidelity. TET1 is found to bind extensively to the genome, particularly at CpG-rich promoters and within genes, where it converts 5-methylcytosine (mC) to 5-hydroxymethylcytosine (hmC). hmC is enriched at transcription start sites (TSSs) and gene bodies, contrasting the distribution of mC. TET1 is also associated with transcriptional repression, binding a significant proportion of Polycomb group target genes and colocalizing with the SIN3A co-repressor complex. The study suggests that TET1 fine-tunes transcription, opposes aberrant DNA methylation at CpG-rich sequences, and contributes to the regulation of DNA methylation fidelity.