Toward a Quadruplet\nCodon Mitochondrial Genetic Code

Nature has evolved to exclusively use a genetic code\nconsisting\nof triplet nucleotide codons. The translation system, however, is\nknown to be compatible with 4-nucleotide frameshift or quadruplet\ncodons. In this study, we begin to explore the possibility of a genome\nmade up entirely of quadruplet codons using the minimal mitochondrial\ngenome of Saccharomyces cerevisiae as\na model system. We demonstrate that mitochondrial tryptophanyl–\nand tyrosyl–tRNAs with modified anticodons effectively suppress\nmutant <i>cox</i><i>3</i> genes containing a TAG\nstop or TAGA quadruplet codon, leading to the production of full-length\nCOX3 and a respiratory-competent phenotype. This work provides a method\nfor introducing heterologous tRNAs into the yeast mitochondria for\ngenetic engineering applications and serves as a starting point for\nthe development of a quadruplet codon genetic code.