Codon wobble positions

Codon usage table of Eschericia coli K12 DH10B. The first three characters are the codon, the second character in parentheses is the amino acid coded for by the codon, and the percentage is the relative usage of that codon in the genome across all CDSs.

The wobble position of a codon refers to the 3rd nucleotide in a codon. This nucleotide has two major characteristics:

1. Binding of a codon in an mRNA the cognate tRNA is much "looser" in the third position of the codon. This permits several types of non-Watson–Crick base pairing to occur at the third codon position.
2. The genetic code is redundant whereby several different codons code for the same amino acid. Often, this redundancy is specified in the third codon position such that several codons with the same first two nucleotides, but different third position nucleotides, code for the same amino acids.

Revised pairing rules

tRNA 5' anticodon base	mRNA 3' codon base
G	U,C
C	G
k2C	A
A	U,C,(A),G
unmodified U	U,(C),A,G
xm5s2U,xm5Um,Um,xm5U	A,(G)
xo5U	U,A,G
I	A,C,U

(Wobble pair table from wikipedia.)