Table 1.

Estimation of the Time Span of the CUG Codon Reassignment

Sc. pombe–Sa. cerevisiae	Sa. cerevisiae– Ca. albicans	CUG Codon Ambiguity	CUG Codon Reassignment
1,850	841a	520–841	740–855
1,144a	730	415–730	605–695
1,144a	841a	440–841	640–740
485	235b	135–235	195–225
587b	360	205–360	295–340
587b	235b	135–235	190–220

Note.—Estimated times in million years for the split between Sa. cerevisiae and Ca. albicans, Sa. cerevisiae and Sc. pombe, and the reassignment of the CUG codon were calculated with a Penalized-likelihood program for the phylogenetic tree generated with RAxML using the WAG + Γ + F model. Time constrains for the splits between Sa. cerevisiae and Ca. albicans, and Sa. cerevisiae and Sc. pombe as reported by ^aHeckman et al. (2001) and ^bDouzery et al. (2004), respectively, were included both individually and combined. For each CUG codon reassignment time computation, constrained time estimates are typed in bold. The CUG codon reassignment time estimates are given as differences between the time estimates for the divergence of Pachysolen tannophilus from the Pichiaceae and Ogataea species (first number), and the first occurrence of the ${\text{tRNA}}_{\text{CAG}}^{\text{Ser}}$ (second number; separation of the CTG clade from the branch containing Pa. tannophilus, the Pichiaceae and Ogataea species). The CUG codon ambiguity time estimates, however, are given as differences between the time estimates for the latest possible fixation of the ${\text{tRNA}}_{\text{CAG}}^{\text{Ser}}$ (first number; separation of Ca. tenuis, the most basal species in the CTG clade) and the earliest possible invention of the ${\text{tRNA}}_{\text{CAG}}^{\text{Ser}}$ (second number; separation of the Saccharomycetaceae and the CTG clade). The time estimate for the divergence of Sc. pombe and Sa. cerevisiae (1,850 Ma) based on the constraint of 841 Ma for the split of Sa. cerevisiae and Ca. albicans predates the emergence of eukaryotes and should be ignored.