New work describes our efforts to achieve CRISPR editing of the mitochondrial genome. biorxiv.org/lookup/content/s… The CRISPR toolbox has revolutionized the study of nuclear DNA, but the mitochondrial genome (mtDNA) has remained out of reach, mainly because there are no known ways to deliver sgRNAs across both outer and inner mitochondrial membranes. Yet many organisms have evolved mechanisms to transport RNAs across their mitochondrial membranes. Trypanosomes, for example, do not encode any tRNAs in their mtDNA, and must import all of them from the cytosol to support intra-mitochondrial protein translation. We started with yeast. We engineered a strain that must repair a STOP codon in mtDNA (an arginine biosynthesis gene) to survive. After screening a library of sgRNA import sequences, we identified one that enables a small degree of functional CRISPR editing in mitochondria. Graduate student Sifei Yin obtained these exciting results several years ago, and spent the intervening time understanding how sgRNA import works, and how to make it better. Read the paper to learn what she uncovered!