Decreased GC Content at the Third Codon Position in CandidaSpecies That Reassigned the CTG Codon From Leucine to Serine
| Candida species | GC content of coding sequences (%) | |||
| Total | 1st codon position | 2nd codon position | 3rd codon position | |
| C. albicans | 36.93 | 44.14 | 37.65 | 29.00 |
| C. dubliniensis | 36.13 | 41.86 | 39.91 | 26.65 |
| C. maltosa | 37.16 | 44.73 | 37.60 | 29.15 |
| C. glabrata | 41.91 | 45.56 | 37.81 | 42.37 |
| S. cerevisiae | 39.71 | 44.59 | 36.58 | 37.96 |
| S. pombe | 39.80 | 48.04 | 38.24 | 33.12 |
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All species shown have similar GC content in coding DNA and also at the first and second codon positions. However, GC pressure decreases significantly at the third codon position (N3, bold) in the three species that decode the standard leucine-CTG codon as serine, that is,Candida albicans, Candida dubliniensis, and Candida maltosa. Candida glabrata decodes the CTG codon as a leucine and follows the Saccharomyces crevisiae andSchizosaccharomyces pombe pattern. An exception to the lowering of GC content at the N3 position in Candida species that reassigned the CTG codon is represented by Candida cylindracea. However, the latter uses the CTG codon at a high frequency, which is in sharp contrast to a generalized low CTG usage in the Candida species that reassigned the CTG codon, indicating that other evolutionary forces shape CTG usage in C. cylindracea.
