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 expression of MAT2A transcripts (PubMed:28525753, PubMed:30197299, PubMed:30197297, PubMed:33428944, PubMed:33930289). Able to N6-methylate a subset of mRNAs and U6 small nuclear RNAs (U6 snRNAs) (PubMed:28525753). In contrast to the METTL3-METTL14 heterodimer, only able to methylate a limited number of RNAs: requires both a 5'UACAGAGAA-3' nonamer sequence and a specific RNA structure (PubMed:28525753, PubMed:30197299, PubMed:30197297). Plays a key role in S-adenosyl-L-methionine homeostasis by mediating N6-methylation of MAT2A mRNAs, altering splicing of MAT2A transcripts: in presence of S-adenosyl-L-methionine, binds the 3'-UTR region of MAT2A mRNA and specifically N6-methylates the first hairpin of MAT2A mRNA, preventing recognition of their 3'-splice site by U2AF1/U2AF35, thereby inhibiting splicing and protein production of S-adenosylmethionine synthase (PubMed:28525753, PubMed:33930289). In S-adenosyl-L-methionine-limiting conditions, binds the 3'-UTR region of MAT2A mRNA but stalls due to the lack of a methyl donor, preventing N6-methylation and promoting expression of MAT2A (PubMed:28525753). In addition to mRNAs, also able to mediate N6-methylation of U6 small nuclear RNA (U6 snRNA): specifically N6-methylates adenine in position 43 of U6 snRNAs (PubMed:28525753, PubMed:29051200, PubMed:32266935). Also able to bind various lncRNAs, such as 7SK snRNA (7SK RNA) or 7SL RNA (PubMed:29051200). Specifically binds the 3'-end of the MALAT1 long non-coding RNA (PubMed:27872311). adenosine in U6 snRNA + S-adenosyl-L-methionine = H(+) + N(6)-methyladenosine in U6 snRNA + S-adenosyl-L-homocysteine an adenosine in mRNA + S-adenosyl-L-methionine = an N(6)-methyladenosine in mRNA + H(+) + S-adenosyl-L-homocysteine Methyltransferase activity is autoinhibited by the K-loop region that blocks S-adenosyl-L-methionine-binding (PubMed:30197297). Upon activation, K-loop changes conformation, allowing S-adenosyl-L-methionine-binding and subsequent methyltransferase activity (PubMed:30197297). mRNA N6-adenosine-methyltransferase activity is inhibited by zinc (PubMed:33428944). Interacts with MEPCE (PubMed:29051200). Interacts with LARP7 (PubMed:29051200). The VCR (vertebrate conserved) regions bind the first hairpin of MAT2A mRNAs (PubMed:28525753). The VCR regions interact with the internal stem-loop within U6 snRNAs, inducing the conformational rearrangement of the A43-containing region of U6 snRNA, thereby modifying the RNA structure to become suitable for productive catalysis by the methyltransferase region (PubMed:32266935). The K-loop region occludes the S-adenosyl-L-methionine-binding pocket (PubMed:30197297). Upon activation, conformation of the K-loop changes, allowing S-adenosyl-L-methionine-binding (PubMed:30197297). Belongs to the methyltransferase superfamily. METTL16/RlmF family. According to a report, N6-methylation of MAT2A affects MAT2A mRNA stability instead of preventing splicing (By similarity). However, it was later shown that N6-methylation of MAT2A transcripts prevents recognition of their 3'-splice site by U2AF1/U2AF35, thereby inhibiting splicing and protein production (PubMed:33930289). Stoichiometry of the protein is unclear. According to two reports, the methyltransferase acts as a monomer (PubMed:30197299, PubMed:30197297). According to a another paper, it acts as a homodimer (PubMed:29593291). Truncated C-terminus.