The function of FASTKD3 (FAST kinase domains 3, ENSG00000124279) is as follows. Required for normal mitochondrial respiration (PubMed:20869947). Increases steady-state levels and half-lives of a subset of mature mitochondrial mRNAs MT-ND2, MT-ND3, MT-CYTB, MT-CO2, and MT-ATP8/6. Promotes MT-CO1 mRNA translation and increases mitochondrial complex IV assembly and activity (PubMed:27789713). .