rRNA N6-methyltransferase that specifically methylates the adenine in position 4220 of 28S rRNA. N6-methylation of adenine(4220) in 28S rRNA is required for translation. adenosine(4220) in 28S rRNA + S-adenosyl-L-methionine = H(+) + N(6)-methyladenosine(4220) in 28S rRNA + S-adenosyl-L-homocysteine Accumulates in the nucleolus, where ribosome biogenesis takes place. The regulatory loop blocks the catalytic center by bridging the methyltransferase domain and the C-terminal CCHC-type zinc finger, resulting in an autoinhibitory conformation. Belongs to the ZCCHC4 family.