RNA N6-methyltransferase that methylates adenosine residues at the N(6) position of a subset of RNAs and is involved in S-adenosyl-L-methionine homeostasis by regulating splicing of S-adenosylmethionine synthase transcripts (sams-3, sams-4 and sams-5). Able to N6-methylate a subset of mRNAs containing the 5'UACAGAAAC-3' nonamer sequence. Plays a key role in S-adenosyl-L-methionine homeostasis: under rich-diet conditions, catalyzes N6-methylation of S-adenosylmethionine synthase mRNAs (sams-3, sams-4 and sams-5), directly inhibiting splicing and protein production of S-adenosylmethionine synthase. In addition to mRNAs, also able to mediate N6-methylation of U6 small nuclear RNA (U6 snRNA). Required for gamete production, inhibiting germ cell proliferative fate and ensuring germ cell meiotic development. Also promotes progression of the mitotic cell cycle in those germ cells that continue to proliferate. Plays a role in the development of the vulva, somatic gonad and embryo. an adenosine in mRNA + S-adenosyl-L-methionine = an N(6)-methyladenosine in mRNA + H(+) + S-adenosyl-L-homocysteine adenosine in U6 snRNA + S-adenosyl-L-methionine = H(+) + N(6)-methyladenosine in U6 snRNA + S-adenosyl-L-homocysteine Self-associates. Interacts with dlc-1; the interaction is direct, and is required for nuclear localization of mett-10. Accumulates in nuclei as cells enter meiosis. During meiotic prophase, expression is predominantly nuclear, but does not co-localize with DNA. Recruited to the nucleus by dlc-1, a component of the dynein complex. Belongs to the methyltransferase superfamily. METTL16/RlmF family.