16S rRNA monitors base-pairing between the codon and the anticodon. Adenine 1493, one of three universally conserved bases in 16S rRNA, forms hydrogen bonds with the bases in both the codon and the anticodon only if the codon and anticodon are correctly paired.

[Information from J. M. Ogle and V. Ramakrishnan, Annu. Rev. Biochem. 74:129–177, 2005, Fig. 2a.]