Superwobbling
Genetic coding
At the base of code evolution, tRNA-34U (wobble U) must be modified by methylation at the 5-carbon (i.e., tRNA-34cnm5U; 5-cyanomethyluridine).
Otherwise, the genetic code could not split into 2 codon sectors.
Sadly, we could only have 16 assignments in the genetic code. We have 21 assignments: 20 amino acids plus stops.
Unmodified wobble tRNA-34U reads mRNA wobble A, G, C and U. This is how 4 codon boxes are read by a single tRNA-34U (anticodon UNN) in mitochondria (N can be almost any base; there are all 4 codon sectors in column 2 (anticodon UGN)). Superwobbling is a mechanism to shrink the size of the mitochondrial genome by reducing the number of needed tRNAs.
So, if tRNA-34U is utilized, tRNA-34U must be modified to support 2 codon sectors (i.e., Phe, Tyr, His, Gln, Asn, Lys, Asp, Glu and Cys).
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