Fas-Activated Serine-Threonine Kinase Domains 5 (FASTKD5) binds 12S rRNA and all mitochondrial mRNAs except MT-ND3 (Antonicka and Shoubridge 2015). Reduced expression of FASTKD5 causes defects in RNA processing that result in the accumulation of MT-ND1, MT-ND2, and MT-CO2 mRNAs and unprocessed H-strand transcripts containing coding regions of MT-CO1, MT-ATP6, MT-ATP8, MT-CO3, MT-ND5, and MT CYTB (Antonicka and Shoubridge 2015, Ohkubo et al. 2021), regions that do not have flanking tRNAs processed by RNase P and RNase Z. FASTKD5 appears to participate in non-canonical mitochondrial RNA processing. Overall, a reduction in FASTKD5 produced a reduction in large and small mitochondrial ribosome subunits (Antonicka and Shoubridge 2015) and respiratory complex IV (Antonicka and Shoubridge 2015, Ohkubo et al. 2021)..