S-adenosyl-L-methionine-dependent methyltransferase that specifically methylates the N(1) position of adenine 2142 in 25S rRNA. N(1)-methyladenine(2142) in 25S rRNA is present in helix 65, a region that accounts for most of the intersubunit surface of the large subunit. adenosine(2142) in 25S rRNA + S-adenosyl-L-methionine = H(+) + N(1)-methyladenosine(2142) in 25S rRNA + S-adenosyl-L-homocysteine Loss of N(1)-methyladenine(2142) in 25S rRNA. Confers anisomycin and peroxide sensitivity to the cells as well as slight defects in ribosome subunit joining. Present with 623 molecules/cell in log phase SD medium. Belongs to the BMT2 family.