Five modified nucleotides have been detected in the 12S rRNA: 5-methylcytidine-841 catalyzed by NSUN4, 6-dimethyladenosine-936 catalyzed by TFB1M, 6-dimethyladenosine-937 catalyzed by TFB1M, 5-methyluridine-429, and 4-methylcytidine-839 (reviewed in Van Haute et al. 2015). Four modified nucleotides have been detected in 16S rRNA: 2'-O-methylguanosine-1145 catalyzed by MRM1, 2'-O-methylguanosine-1370 catalyzed by RNMTL1 (MRM3), 2'-O-methyluridine-1369 catalyzed by FTSJ2 (MRM2), and pseudouridine-1397. 2'-O-methyluridine-1369 and 2'-O-methylguanosone-1370 occur in the A-loop of rRNA which is located at the peptidyl transferase center of the large subunit. Here the modified residues play a role in interaction with the aminoacyl site of tRNA. Knockouts of TFB1M and NSUN4 are lethal in mice and mutations in TFB1M may be related to aminoglycoside-induced deafness (reviewed in Van Haute et al. 2015).