Plays a role in the import of cytosolically synthesized preproteins into mitochondria. Binds the mature portion of precursor proteins. Interacts with cellular components, and possesses weak ATPase activity. May be a chaperone-like protein that helps to keep newly synthesized precursors in an unfolded import compatible state (By similarity). Interacts with HSP90A, VCP, ATP6V1D, KIAA0665, AMPK, and DMAP1 through its TPR repeat. Isoforms 1 and 2 are produced by 2 alternative initial coding exons with very similar sequences which differ at only 4 positions. Isoform 1 is ubiquitously expressed while isoform 2 is expressed only in mature testicular germ cells. Isoform 1 is expressed in all testicular cells. Isoform 2 is highly expressed in early to late pachytene cells but expression is significantly decreased in round spermatid cells. Isoform 2 is hardly detectable in testis at 1 week post partum but expression gradually increases for 2 to 4 weeks post partum. Isoform 1 is detected during this period but its expression does not change. Mice are viable, grow normally and both males and females are fertile. There is no effect on spermatogenesis or protein import into mitochondria. Belongs to the Tom34 family.