Table 1.
The accuracy of RF1: The fold decrease in kcat/KM for RF1 at codons differing from RF1 stop codons (UAA and UAG) by 1 nt in the presence or absence of RF3
| Codon | Fold decrease in kcat/KM (×10−3)
|
|||||
|---|---|---|---|---|---|---|
| −RF3 | (σ) | +RF3 | (σ) | |||
| AAA | * | * | ||||
| AAG | * | * | ||||
| GAA | * | 400 | 100 | |||
| GAG | * | 600 | 300 | |||
| CAA | 400 | 100 | 90 | 20 | ||
| CAG | 500 | 100 | 90 | 10 | ||
| UGA | 136 | 7 | 37 | 2 | ||
| UGG | 47 | 5 | 11 | 1 | ||
| UCA | 15 | 2 | 4.1 | 0.1 | ||
| UCG | 19 | 1 | 5.1 | 0.4 | ||
| UUA | 26 | 2 | 7.6 | 0.4 | ||
| UUG | 13 | 2 | 3.6 | 0.4 | ||
| UAC | 20 | 1 | 5.6 | 0.6 | ||
| UAU | 1.1 | 0.3 | 0.4 | 0.1 | ||
A high value for the fold decrease in kcat/KM means that the accuracy is high. For example, from this table, the codon UCG is read by RF1 19,000 times less efficiently (in the absence of RF3) than RF1 reads the stop codon UAA. The results are the mean of three experiments with SD of the mean (σ). Unresolvable values are represented by *, where release is too slow in relation to peptidyl-tRNA dissociation to be measurable. The fold change in kcat/KM for these points is greater than 106. Bases in bold are those that differ from the sequence of a normal stop codon.