Aminoglycoside resistance 16S rRNA methyltransferases block endogenous methylation, affect translation efficiency and fitness of the host

MALDI MS analysis of NpmA methylation in 16S rRNA fragment C1378–G1432. (A) Spectrum of RNase T1 rRNA from E. coli MM294/pGB2ΩnpmA. The empirical m/z values are given above the peaks and match the theoretical masses (see below) to within 0.1 Da. (Inset) Higher mass region of rRNA showing the monomethylated C1406–G1415 fragment. (B) MALDI tandem MS of RNase A nucleotides from E. coli MM294/pGB2ΩnpmA. The CACp fragment (positions 1407–1409) at m/z 970 was selected and subjected to further fragmentation. Peaks corresponding to C (d₁), CmA (a₂), and mACp (Y₂) are indicated. (C) Theoretical masses of the monoisotopic E. coli RNase T1 fragments with 3′-linear phosphate (p). Only fragments that are tetranucleotides and larger are shown.