Table 15-1 Amino Acid Incorporation into Proteins Sum of Observed Tentative Calculated Triplet Frequency Calculated Amino acid Codon Triplet Amino acid Incorporation Assignments 3A 2AIC 1A2C 30 Frequencies Poly ac (5: 1) asparagine 24 2AIC Glutamine 24 2AIC Histidine 1A2C 4.0 Lysine 100 3A 100 Proline 1A2C, 3C 4.0 0.8 4.8 Threonine 2AIC. 1A20 4.0 Poly AC (1: 5) Asparagine 2AIC 3.3 Glutamine 5 2AIC 3.3 Histidine 1A2C 16.7 16.7 Lysine 1 3A 0.7 0.7 Proline 1A2C, 3C 16.7 83.3 100 Threonine 21 2AIC, 1A2C 3.3 16.7 20 The amino acid incorporation into proteins was observed after adding random copolymers of A and C to a cell-free extract similar to that described in Figure 15-1. The incorporation is given as a percentage of the maximal incorporation of a single amino acid. The copolymer ratio was then used to calculate the frequency with which a given codon would appear in the polynucleotide product. The relative frequencies of the codons are a function of the probability that a particular nucleotide will occur in a given position of a codon. For example, when the A/C ratio is 5: 1. the ratio of AAA/AAC=5x5x 5: 5 X5x 1=125: 25. If we thus assign to the 3A codon a frequency of 100, then the 2A and 1c codon is assigned a frequency of 20. By correlating the relative frequencies of amino acid incorporation with the calculated frequencies with which given codons appear, tentative codon assignments can be madeComposition of triplets coding for certain amino acids were assigned