NSUN4 Is a Dual Function Mitochondrial Protein Required for Both Methylation of 12S rRNA and Coordination of Mitoribosomal Assembly

Abstract

Biogenesis of mammalian mitochondrial ribosomes requires a concerted maturation of both the small (SSU) and large subunit (LSU). We demonstrate here that the m5C methyltransferase NSUN4, which forms a complex with MTERF4, is essential in mitochondrial ribosomal biogenesis as mitochondrial translation is abolished in conditional Nsun4 mouse knockouts. Deep sequencing of bisulfite-treated RNA shows that NSUN4 methylates cytosine 911 in 12S rRNA (m5C911) of the SSU. Surprisingly, NSUN4 does not need MTERF4 to generate this modification. Instead, the NSUN4/MTERF4 complex is required to assemble the SSU and LSU to form a monosome. NSUN4 is thus a dual function protein, which on the one hand is needed for 12S rRNA methylation and, on the other hand interacts with MTERF4 to facilitate monosome assembly. The presented data suggest that NSUN4 has a key role in controlling a final step in ribosome biogenesis to ensure that only the mature SSU and LSU are assembled.

NSUN 3 and ABH 1 modify the wobble position of mt‐t RNA Met to expand codon recognition in mitochondrial translation

“…DNMT2 mainly catalyses the m 5 C modification in position 38 of tRNA Asp in human cells (Goll et al , 2006), while the so far characterised NSUN proteins show specificity for tRNAs (NSUN2, NSUN6; Schaefer et al , 2010; Tuorto et al , 2012; Blanco et al , 2014; Haag et al , 2015a) or rRNA (NSUN1/NOP2, NSUN5; Sloan et al , 2013; Tafforeau et al , 2013; Schosserer et al , 2015). NSUN2 can also modify vault RNAs and mRNAs (Hussain et al , 2013), and NSUN4 was described to localise to mitochondria where it was shown to methylate the mitochondrial 12S rRNA in mice (Cámara et al , 2011; Metodiev et al , 2014). …”

NSUN6 is a human RNA methyltransferase that catalyzes formation of m5C72 in specific tRNAs

“…In humans, knockdown of NSUN1 causes severe pre-rRNA processing defects, whereas depletion of NSUN5 leads to only mild defects in the biogenesis of the large ribosomal subunit (Sloan et al 2013;Tafforeau et al 2013;Schosserer et al 2015). Another member of the NSUN family, NSUN4 was recently found to localize to mitochondria and to methylate C911 in the mitochondrial 12S rRNA in mice (Metodiev et al 2014). NSUN4 interacts with the mitochondrial transcription termination factor MTERF4 and this interaction is essential for mitochondrial ribosome assembly (Cámara et al 2011;Metodiev et al 2014).…”

“…Another member of the NSUN family, NSUN4 was recently found to localize to mitochondria and to methylate C911 in the mitochondrial 12S rRNA in mice (Metodiev et al 2014). NSUN4 interacts with the mitochondrial transcription termination factor MTERF4 and this interaction is essential for mitochondrial ribosome assembly (Cámara et al 2011;Metodiev et al 2014).…”

Post-transcriptional modifications in development and stem cells

“…1) (Metodiev et al, 2014;Nakano et al, 2016;Schosserer et al, 2015;Sharma et al, 2013;Van Haute et al, 2016). The methylase activity of NSUN7 has not been confirmed; however, its interaction with enhancer RNAs (eRNAs) can influence the transcription of the eRNA-targeted genes (Aguilo et al, 2016).…”

“…For instance, loss of NSUN1-and NSUN4-mediated methylation of rRNA affects prerRNA processing, ribosome biogenesis and polysome assembly (Metodiev et al, 2014;Sharma et al, 2013). By contrast, lack of NSUN5-dependent methylation relaxes rRNA structure in the vicinity of the peptidyltransferase centre and alters the translation fidelity of the ribosome during stress responses in yeast (Fig.…”