The impact of a codon reassignment event on the evolution of the yeast C.cylindracea

Abstract

The genetic code is degenerate allowing for introduction of species specific codon utilization biases. These has been intensively studied but it is not yet clear whether they arise from mutational pressure alone or whether other forces, such as the translational efficiency, also influence it To address this question we took advantage of a unique genetic code alteration that occurred in the fungal Saccharomycotina subphylum, the so called CTG clade, which translate leucine CTG codons as serine due to a novel transfer RNA tRNACAGSer The atypical serine CTG codons are rarely used among the CTG clade species except for Candida cylindracea which uses CTGs at high level, allowing to gain further insight on how they were remodeled after the reassignment event For this, we conducted de novo whole genome sequencing, and annotation of C cylindracea. Alongside, we performed systematic alignment of yeast orthologous genes, phylogenetic reconstruction and codon evolution analysis The results showed that C cylindracea’s genome is different from the other Saccharomycotina genomes and occupies a basal position with respect to the reassignment event. Our findings support the hypothesis that CTG codon reassignment, and not only G+C pressure, exerted a strong influence on serine/leucine codon evolution in yeast.