The role of nucleotide modifications in the yeast mitochondrial ribosome.

Post-transcriptionally modified nucleotides in ribosomal RNA, and the modifying enzymes themselves, could influence the assembly, structure, and function of the ribosome. The PET56 gene in yeast encodes the enzyme responsible for formation of 2'-O-methylguanosine at a specific nucleotide in the peptidyl transferase center of the mitochondrial large subunit ribosomal RNA. While PET56 is normally essential for the formation of functional mitochondrial ribosomes, extragenic mutations have been obtained that suppress, albeit weakly, pet56 loss-of-function mutations. Thus neither the Pet56p-catalyzed ribose methylation nor the Pet56 protein itself is absolutely required for the synthesis of a functional ribosome.