EVOLUTIONARY ORIGIN OF NONUNIVERSAL CUG(SER) CODON IN SOME CANDIDA SPECIES AS INFERRED FROM A MOLECULAR PHYLOGENY

CUG, a universal leucine codon, has been reported to be read as serine in various yeast species belonging to the genus Candida. To gain a de eper insight into the origin of this deviation from the universal gene tic code, we carried out a phylogenetic analysis based on the small-su bunit ribosomal RNA genes from some Candida and other related Hemiasco mycetes. Furthermore, we determined the phylogenetic relationships bet ween the tRNA(Ser)CAG, responsible for the translation of CUG, from so me Candida species and the other serine and leucine isoacceptor tRNAs in C. cylindracea. We demonstrate that the group of Candida showing th e genetic code deviation is monophiletic and that this deviation could have been originated more than 150 million years ago. We also describ e how phylogenetic analysis can be used for genetic code predictions.