CGG Codon

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Comparison of E. coli and Mesoplasma florum with unnatural amino acid incorporation. E coli can use a freed TAG codon. Mesoplasma florum can possibly use an absent CGG codon.

Due to the evolution of progressively more AT rich genome, the Mycoplasmas have begun to evolve to use the CGG arginine codon less frequently. In fact, in Mycoplasma capricolum it appears the codon has completely disappeared [1]. However, in 1995, a paper was published finding that CGG was used in Mycoplasma hyopneumoniae [2] casting doubts on the applicability of this finding to other Mycoplasmas.

A codon usage analysis of the codons in Mycoplasma capricolum [3] and codons in Mycoplasma hyopneumoniae [4] show an interesting pattern. The total quantity of CGG codons found in Mycoplasma capricolum total 6 (likely from unexpressed genes; need software to find exact genes), while in Mycoplasma hyopneumoniae there are 686, over a hundred-fold difference. One can infer that Mycoplasma mycoides also has an unassigned CGG codon [5] since it can be transplanted into Mycoplasma capricolum successfully [6].

Mesoplasma florum, like Mycoplasma capricolum, only has 6 CGG codons [7] , and therefore it seems possible that Mesoplasma florum also has an unassigned CGG codon, one that could possibly be used for unnatural amino acid (UAA) incorporation. This could simplify UAA incorporation or be used to help create a new genomic code.


  1. Takanori Oba et al (1990). "CGG: An unassigned or nonsense codon in Mycoplasma capricolum". PNAS. [1]
  2. Satoshi Futo et al (1995). "Molecular Cloning of a 46-Kilodalton Surface Antigen (P46) Gene from Mycoplasma hyopneumoniae: Direct Evidence of CGG Codon Usage for Arginine". Journal of Bacteriology. [2]
  3. Codon Usage Database. "Mycoplasma capricolum subsp. capricolum ATCC 27343 [gbbct]: 823 CDS's (300348 codons)". [3]
  4. Codon Usage Database. "Mycoplasma hyopneumoniae 7448 [gbbct]: 698 CDS's (267105 codons)". [4]
  5. Codon Usage Database. "Mycoplasma mycoides subsp. mycoides SC str. PG1 [gbbct]: 1016 CDS's (330592 codons)". [5]
  6. Carole Lartigue et al (2007). "Genome Transplantation in Bacteria: Changing One Species to Another". Science. [6]
  7. Codon Usage Database. "Mesoplasma florum L1 [gbbct]: 683 CDS's (245761 codons)". [7]