The translation of the mRNA encoding E. coli\'s threonine aminoacyl tRNA synthet

Question

The translation of the mRNA encoding E. coli's threonine aminoacyl tRNA synthetase is regulated similarly to the mechanism used for balacing expression of ribosomal proteins relative to the ribosomal RNA they bind. Propose a model that would explain how threonine aminoacyl tRNA synthetase protein levels are balanced to match levels of threonine tRNA.

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Explanation / Answer

See, before translation to start, amino acids are activated by adenylation; so is threonine to form. Adenylation means a reaction between an amino acid, threonine and ATP molecule to form threonyl-AMP. The next step is addition of this threonyl-AMP to a tRNA to form threonyl-tRNA.

Both the above steps are catalysed by the enzyme, threonyl-tRNA synthase.

Now, if we have to prove, that the levels of threonyl-tRNA synthase are balanced to match levels of threonyl-tRNA; then we can do this by removing tRNA from the reaction mixture. Threonyl-AMP is tightly bound to threonyl-tRNA synthase by non covalent interactions, and AMP is not removed until it gets a tRNA molecule. By stopping the reaction, in between, we can calculate the level of complex:- threonyl-tRNA synthase bound to threonyl-AMP. Then add equivalent amount of tRNA to the reaction mix in the next step. You will find that the level of threonine tRNA formed is directly proportional to the concentration of enzyme-substrate complex shown above (in bold).

Second way to prove this by use of free energy of reactions.

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