Enables N6-isopentenyladenosine methylthiotransferase activity. Acts upstream of or within mitochondrial tRNA modification; positive regulation of mitochondrial translation; and positive regulation of translational fidelity. Located in mitochondrion. Is expressed in several structures, including adenohypophysis; alimentary system; nose; trigeminal ganglion; and vibrissa. Orthologous to human CDK5RAP1 (CDK5 regulatory subunit associated protein 1). [provided by Alliance of Genome Resources, Apr 2022]