Plays an important role in assembly of the mitochondrial large ribosomal subunit. As a component of a functional protein-RNA module, consisting of RCC1L, NGRN, RPUSD3, RPUSD4, TRUB2, FASTKD2 and 16S mitochondrial ribosomal RNA (16S mt-rRNA), controls 16S mt-rRNA abundance and is required for intra-mitochondrial translation. May play a role in mitochondrial apoptosis. Monomer. Found in a complex with GRSF1, DDX28, DHX30 and FASTKD5. Associates with the 16S mitochondrial rRNA (16S mt-rRNA). Forms a regulatory protein-RNA complex, consisting of RCC1L, NGRN, RPUSD3, RPUSD4, TRUB2, FASTKD2 and 16S mt-rRNA. Localizes to mitochondrial RNA granules found in close proximity to the mitochondrial nucleoids. Belongs to the FAST kinase family.