Transfer RNAs, commonly called tRNAs, are essential molecules that help cells build proteins. Before they can perform this job, many tRNAs undergo small chemical changes called base modifications. These modifications help the molecules fold correctly, remain stable, and accurately translate genetic information into proteins.

Scientists have identified many of these modifications, but the complete map of modified bases in mitochondrial tRNAs has remained incomplete. Mitochondria are the energy-producing structures inside cells, and defects in mitochondrial tRNAs have been linked to a variety of human diseases.

Researchers at the University of Oregon used Nanopore direct RNA sequencing to create one of the most comprehensive maps of base modifications in yeast mitochondrial tRNAs to date. Yeast is widely used as a model organism because many aspects of its mitochondrial biology are similar to those of humans.

Unlike traditional sequencing methods that often require RNA to be converted into DNA before analysis, Nanopore direct RNA sequencing reads RNA molecules directly. This approach makes it easier to detect many naturally occurring chemical modifications that would otherwise be difficult to identify.

The researchers also adapted a technique called D-seq to detect a specific modification known as dihydrouridine. By combining Nanopore RNA sequencing, D-seq, and genetically engineered yeast lacking individual RNA-modifying enzymes, they were able to determine which enzymes create several important modifications within mitochondrial tRNAs.

Their work identified the enzymes Dus1 and Dus2 as being responsible for producing multiple dihydrouridine modifications. The researchers also discovered that these modifications do not act independently. Instead, they found evidence that several modification enzymes influence one another, creating interconnected networks that help shape the final structure of mitochondrial tRNAs.

Another important finding involved two additional RNA modifications, pseudouridine and methylated uridine. The results suggest that one modification can promote the formation of another, demonstrating that mitochondrial tRNA maturation is a coordinated process rather than a series of isolated chemical events.

Creating a comprehensive map of these modifications provides researchers with a valuable reference for future studies. Because many human mitochondrial diseases result from defects in mitochondrial tRNAs, understanding how these modifications normally occur may help scientists better understand how disease develops.

The study also highlights the growing power of Nanopore RNA sequencing for investigating RNA biology. As direct RNA sequencing technologies continue to improve, they are allowing researchers to study RNA molecules in greater detail, including chemical modifications that influence how cells function but cannot be detected through conventional sequencing methods.

Although the research was performed in yeast, the findings provide important insights into mitochondrial RNA biology and establish a stronger foundation for investigating mitochondrial disorders in humans.