Plant DNA methyltransferases and uses thereof

A mammalian cell comprising an expression vector which comprises a polynucleotide encoding a fusion protein, said fusion protein comprising a DNA targeting moiety linked to a catalytic domain of a plant DNA methyltransferase 3 (DNMT3) protein, wherein the cell comprises a gene and a regulatory sequence thereof, that has a higher methylation status at a CHH site than a methylation status at said CHH site of said gene in the absence of the fusion protein, wherein said DNMT3 is not a domain rearranged methyltransferase (DRM).