ATP-dependent cytosine methylase that maintains DNA methylation by acting at hemimethylated palindromic 5'-CG-3' sites to produce symmetrically methylated DNA strands (PubMed:24630728, PubMed:31955845, PubMed:32437639). DNA methylation may play a role in transcriptional silencing, particularly at transposable elements (PubMed:24630728). a 2'-deoxycytidine in DNA + ATP + H2O + S-adenosyl-L-methionine = a 5-methyl-2'-deoxycytidine in DNA + ADP + 2 H(+) + phosphate + S-adenosyl-L-homocysteine Hemimethylated DNA substrates stimulate ATP hydrolysis and this is a prerequisite for methyltransferase activity. kcat is 5.0 min(-1) for ATP (in the presence of unmethylated DNA and at 23 degrees Celsius) (PubMed:32437639). kcat is 11.1 min(-1) for ATP (in the presence of hemimethylated DNA and at 23 degrees Celsius) (PubMed:32437639). Interacts with SWI6. Localizes to heterochromatin characterized by trimethylation of histone H3 'Lys-9'. The chromo domain is involved in binding heterochromatin at histone H3 tails methylated on 'Lys-9'. The helicase ATP-binding domain contributes to identifying hemi-methylated CG DNA motifs. The SAM-dependent MTase C5-type domain is involved in hemimethylated DNA binding. Abolishes localization of DMT5 to DNA and abolishes methylation of the fifth carbon of cytosine (5mC) in DNA (PubMed:31955845, PubMed:24630728). Abnormal distribution of histone H3 'Lys-9' methylation (PubMed:31955845). Sensitive to thiabendazole (PubMed:31955845). In the N-terminal section; belongs to the class I-like SAM-binding methyltransferase superfamily. C5-methyltransferase family. In the C-terminal section; belongs to the SNF2/RAD54 helicase family.