Mitochondrial ribosome assembly is a complex multi-step process involving many additional factors. Ribosome formation differs in various groups of organisms. However, there are universal steps of assembly and conservative factors that have been retained in evolutionarily distant taxa. METTL17, the object of the current study, is one of these conservative factors involved in mitochondrial ribosome assembly. It is present in both bacteria and the mitochondria of eukaryotes, in particular mice and humans. In this study, we tested a hypothesis of putative METTL17 methyltransferase activity. MALDI-TOF mass spectrometry was used to evaluate the methylation of a putative METTL17 target - a 12S rRNA region interacting with METTL17 during mitochondrial ribosome assembly. The investigation of METTL17 and other mitochondrial ribosome assembly factors is of both fundamental and practical significance, because defects in mitochondrial ribosome assembly are often associated with human mitochondrial diseases.