NpmA methyltransferase, molecular model. Methyltransferase enzymes act to add methyl groups to nucleic acids such as DNA (deoxyribonucleic acid), a process called DNA methylation. This can silence and regulate genes without changing the genetic sequence. These enzymes can also act on RNA (ribonucleic acid), with NpmA methylating 16S rRNA. NpmA is being studied for its ability to confer antibiotic resistance (specifically resistance to aminoglycosides) in bacteria.