Mitochondrial gene expression is controlled largely through the action of products of the nuclear genome. The yeast nuclear gene suv3 has been implicated in a variety of mitochondrial posttranscriptional processes and in translation and, thus, represents a key control element in nuclear-mitochondrial interactions. We have exploited a property of a mutant allele of suv3, SUV3-1, that causes, among other effects, a massive increase in the abundance of excised group I introns to clone the wild-type gene by a strategy of colony Northern hybridization. We have determined that the 84-kDa deduced protein product of the suv3 gene, which maps to chromosome XVI, has a typical mitochondrial targeting presequence and additional sequence motifs that suggest that it belongs to a family of ATP-dependent RNA helicases, enzymes whose importance in post-transcriptional and translational events has recently become apparent. We have identified the SUV3-1 mutation as a G----T transversion that creates a Val----Leu substitution in a 10-amino acid block that is highly conserved among ATP-dependent RNA helicases. We discuss some implications of this mutation on the effects of the SUV3-1 allele on mitochondrial RNA metabolism.