CODON USAGE IN KLUYVEROMYCES-LACTIS AND IN YEAST CYTOCHROME C-ENCODING GENES

Codon usage (CU) in Kluyveromyces lactis has been studied. Comparison of CU in highly and lowly expressed genes reveals the existence of 21 optimal codons; 18 of them are also optimal in other yeasts like Sacch aromyces cerevisiae or Candida albicans. Codon bias index (CBI) values have been recalculated with reference to the assignment of optimal co dons in K. lactis and compared to those previously reported in the lit erature, taking as reference the optimal codons from S. cerevisiae. A new index, the intrinsic codon deviation index (ICDI), is proposed to estimate codon bias of genes from species in which optimal codons are not known; its correlation with other index values, like CBI or effect ive number of codons (Nc), is high. A comparative analysis of CU in si x cytochrome-c-encoding genes (CYC) from five yeasts is also presented and the differences found in the codon bias of these genes are discus sed in relation to the metabolic type to which the corresponding yeast s belong. Codon bias in the CYC from K. lactis and S. cerevisiae is co rrelated to mRNA levels.