Figure 4-27

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   The first and second bases in an mRNA codon form Watson-Crick base pairs with the third and second bases, respectively, of a tRNA anticodon

However, the base in the third (or wobble) position of an mRNA codon often forms a nonstandard base pair with the base in the first (or wobble) position of a tRNA anticodon. Wobble pairing allows a tRNA to recognize more than one mRNA codon (top); conversely, it allows a codon to be recognized by more than one kind of tRNA (bottom), although each tRNA will bear the same amino acid. Note that a tRNA with I (inosine) in the wobble position can “read” (become paired with) three different codons (see Figure 4-28), and a tRNA with G or U in the wobble position can read two codons. Although A is theoretically possible in the wobble position of the anticodon, it is almost never found in nature.