Mitochondrial transporter that imports/exports pyrimidine nucleotides into and from mitochondria. Selectively transports cytosine, guanosine, inosine and uridine (deoxy)nucleoside mono-, di-, and triphosphates by antiport mechanism. Catalyzes uniport at much lower rate (PubMed:25320081). May import (deoxy)nucleoside triphosphates in exchange for intramitochondrial (deoxy)nucleoside mono- and diphosphates, thus providing precursors necessary for de novo synthesis of mitochondrial DNA and RNA while exporting products of their catabolism (PubMed:25320081). Participates in mitochondrial genome maintenance, regulation of mitochondrial membrane potential and mitochondrial respiration.