Plays an important role in assembly of the mitochondrial large ribosomal subunit (PubMed:25683715). 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 (PubMed:25683715, PubMed:26370583, PubMed:27667664). May play a role in mitochondrial apoptosis. {ECO:0000269|PubMed:18771761, ECO:0000269|PubMed:25683715, ECO:0000269|PubMed:26370583, ECO:0000269|PubMed:27667664}. This is the function of FASTKD2 (FAST kinase domains 2, Ensembl gene identifier ENSG00000118246).