Figure 1.

The secondary structure of the decoding center in the E. coli 16S rRNA and the enzymatic formation of m⁴Cm1402. (A) The secondary structure of the E. coli 16S rRNA is shown on the left. Helix 44 and surrounding regions are shown on the right, with helix and base numbers indicated. A number of modified nucleosides including 5-methylcytidine (m⁵C), N⁴, 2′-O-dimethylcytidine (m⁴Cm) and 3-methyluridine (m³U) are also shown. The bases annotated as A-site (blank circle), P-site (shaded with light gray) and E-site (shaded with dark gray) are indicated (4,6). (B) Enzymatic formation of m⁴Cm1402. N⁴-methylation and 2′-O-methylation of C1402 are catalyzed by RsmH and RsmI, respectively, using Ado-Met as a methyl group donor. After the reaction, Ado-Met is converted to Ado-Hcy.