CpG site-specific alteration of hydroxymethylcytosine to methylcytosine beyond DNA replication

► An episomal vector-based system to monitor cytosine modification was prepared. ► Bisulfite-resistant cytosines at the hydroxymethylated CpG sites, but not non-CpG sites, after DNA replication were observed. ► Bisulfite-resistant cytosines in the CpG sites on episomal vector were mainly methylated CpGs.