Is there selection against wobble in codon-anticodon pairing?

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Science  10 Dec 1976:
Vol. 194, Issue 4270, pp. 1173-1174
DOI: 10.1126/science.996548


Among amino acid codons that require a third-position pyrimidine, there is a significant bias favoring the use of cytidine over uracil in MS2 phage RNA. This could arise from selection against wobble pairing in the interaction of transfer RNA and messenger RNA. Among amino acid codons with fourfold degeneracy, there is a bias favoring pyrimidines over purines.