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This paper addresses the question: can unnatural amino acids be successfully incorporated into the mouse genome in a temporally and spatially specific manner? Han and his associates claim that (1) they have developed a system for incorporation of unnatural amino acid incorporation, (2) the acetylation they induce is spatially and temporally specific, and (3) that this technology will allow researchers to develop better in vivo studies of how cellular proteins affect physiology and disease. In this review, I will contest all three claims. Specifically, I will show that claims 1 and 2 are only qualitatively true: there is no proof that these things happen on a quantitative scale which is relevant for modeling disease, and that there are …show more content…

The work minimally advances the field. Briefly, it shows that unnatural amino acid incorporation is possible in mice. However, it does not do this in a model system which is interesting to study. The introduction mildly alludes to the fact that aberrant or unconventional amino acid acetylation can lead to cancer, but there is no follow up to see if the epigenetic changes which they induce are prevalent enough to cause a change in phenotype. If the purpose of this technology is to model diseases related to epigenetic changes and to see how we might counteract these changes, then that should be part of the proof-of-concept work included in the article. To demonstrate the feasibility of unnatural amino acid incorporation in a mammalian system, the researchers first perform work in cultured cells. Basically, they inserted a vector with the modified tRNA synthetase into first human (HEK293T) cells, and then mouse cells (NIH3T3). The expression of the plasmid vector is dependent on human elongation factor 1, an endogenous protein. Another vector was transformed into the cells containing the sequence for a recombinant GFP protein with the unnatural, acetylated amino acid at position 39. The GFPuv, as it’s called, will only be expressed if the tRNA synthetase recognizes the amber codon (codon which usually causes a stop in transcription) in the protein and appropriately adds

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