A cluster analysis of codon usage in 110 yeast genes (mainly Saccharomyces cerevisiae) reveals two distinct groups: highly expressed genes and lowly expressed genes. Highly expressed genes show a more extreme preference for certain synonymous codons, with a stronger correlation to tRNA abundance and a greater third base pyrimidine bias. These genes also exhibit less A+T richness compared to the yeast genome. The cluster analysis can predict gene expression levels based on codon usage patterns and identifies the codon usage likely to optimize gene expression in yeast. The study shows that codon usage in yeast is influenced by tRNA abundance and the energy of tRNA-mRNA interactions. Highly expressed genes have a more pronounced codon bias, which is consistent with the idea that natural selection favors codons that match abundant tRNAs. The results suggest that codon usage patterns can be used to predict gene expression levels and optimize gene expression in yeast. The study also highlights the importance of codon usage in gene expression and its potential applications in biotechnology.A cluster analysis of codon usage in 110 yeast genes (mainly Saccharomyces cerevisiae) reveals two distinct groups: highly expressed genes and lowly expressed genes. Highly expressed genes show a more extreme preference for certain synonymous codons, with a stronger correlation to tRNA abundance and a greater third base pyrimidine bias. These genes also exhibit less A+T richness compared to the yeast genome. The cluster analysis can predict gene expression levels based on codon usage patterns and identifies the codon usage likely to optimize gene expression in yeast. The study shows that codon usage in yeast is influenced by tRNA abundance and the energy of tRNA-mRNA interactions. Highly expressed genes have a more pronounced codon bias, which is consistent with the idea that natural selection favors codons that match abundant tRNAs. The results suggest that codon usage patterns can be used to predict gene expression levels and optimize gene expression in yeast. The study also highlights the importance of codon usage in gene expression and its potential applications in biotechnology.