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Chapter 14 : Functional Aspects of the Three Modified Nucleotides in Yeast Mitochondrial Large-Subunit rRNA
This chapter focuses on the possible functional significance of the three highly conserved modified nucleotides in the otherwise minimally modified yeast mitochondrial large-subunit rRNA (LSU rRNA). The three modified nucleotides in yeast mitochondrial LSU rRNA, Gm2270, Um2791, and pseudouridine 2819, are equivalent to the Gm2251, Um2552, and pseudouridine 2580, respectively, in peptidyl transferase center (PTC) of Escherichia coli LSU rRna. The PET56 nuclear gene encodes an rRNA ribose methyltransferase (Pet56p) required for the formation of 2’-O-methylguanosine at G2270 in yeast mitochondrial LSU rRNA (G2251 in E. coli numbering), and PET56 function is essential for the formation of functional mitochondrial ribosomes. While PET56 is normally essential for the formation of functional yeast mitochondrial ribosomes, a dominant extragenic mutation has been isolated (SRM1-1) that suppresses, albeit very weakly, pet56 loss-of-function mutations without restoring methylation at G2270 in yeast mitochondrial LSU rRNA. The presence of only three modified nucleotides at highly conserved positions in the PTC of yeast mitochondrial LSU rRNA has fueled speculation that these particular modification might have special functional significance. The recent progress in the identification of genes responsible for specific modifications in E. coli, yeast mitochondrial, and yeast cytoplasmic rRNAs will accelerate the genetic analysis of rRNA modification in these systems. It will be particularly informative to compare the in vivo effects of depleting pseudouridine 2580 in E. coli and yeast mitochondria and Gm2251 and Um2552 in all three ribosomal systems.
Key Concept Ranking
- Small Nucleolar RNA