Table 1.

Crick's wobble rules for calculating W_i

	Codon third position		Anticodon first position	Wi
i	U	j	I	$(1-s_{U:I})\text{tGC}{\text{N}}_{i,j}+(1-s_{U:G})\text{tGC}{\text{N}}_{i,j+1}$
i + 1	C	j + 1	G	$(1-s_{C:G})\text{tGC}{\text{N}}_{i+1,j+1}+(1-s_{C:I})\text{tGC}{\text{N}}_{i+1,j}$
i + 2	A	j + 2	U	$(1-s_{A:U})\text{tGC}{\text{N}}_{i+2,j+2}+(1-s_{A:I})\text{tGC}{\text{N}}_{i+2,j}$
i + 3	G	j + 3	C	$(1-s_{G:C})\text{tGC}{\text{N}}_{i+3,j}+(1-s_{G:U})\text{tGC}{\text{N}}_{i+2,j+2}$

The W_i values are calculated based on Equation (1). The 64 codons are clustered in the genetic code into 16 groups, each one consists of four codons. The four codons in each group differ only in their third position (the wobble position). The formulas for calculating the W_i values for each of the four codons in the group are given in the table. i denotes the index of the codon in the quartet which ends with U, i + 1, i + 2, and i + 3 denote the three other codons which end with bases C, A, and G, respectively. j denotes the index of the tRNA whose anticodon starts with I; all base pairing between the ith codon and the jth anticodon are WC. j + 1, j + 2, and j + 3 denote the three other tRNAs whose anticodons start with bases G, U, and C, respectively. tGCN_ij represents the tRNA gene copy number corresponding to the interaction between the ith codon and the jth tRNA. For each codon, W_i sums over all tRNAs that can pair with the codon. For example, the GCU codon which ends with U can either pair with anticodons that start with I (IGC) and generate a standard WC base pairing, or pair with anticodons that start with G (GGC) and generate a wobble base pairing.