Translation

ID #2413

I was wondering what allows a prokaryotic cell to tell the difference between a tRNA molecule that is meant to be charged with fmet and one that is meant to be charged with regular met. They have the same anitcodon so I don't understand how Aminoacyl tRNA synthetase can tell the difference between a Met tRNA and a fMet tRNA. I also don't understand how the ribosome differentiates between the two when initiating and elongating a polypeptide.


Excellent questions! I can't answer your questions as thoroughly as I would like, but I can definitely address them. The tRNA that is supposed to be charged with fMet differs from a tRNA that is supposed to be charged with regular Met. I don't know exactly how it differs (since it has the same anticodon of 3'-UAC-5') but it is distinct from tRNAs charged with regular Met. In fact, fMet tRNAs are initially charged with regular methionine, and then the formyl group is added later by a different enzyme. (So it is something about the tRNA itself that signals that the methionine should be formylated and the aminoacyl tRNA synthetase may not even distinguish between the two- it always adds Met). In terms of how the ribosome can tell the difference between a regular Met and an fMet, I would imagine that the process of initiation plays a role in that. There are multiple initiation factors involved in the start of translation, and the fMet tRNA always goes into what will be the P site in the small ribosomal subunit instead of the A site. The initation factors may help direct the initiator tRNA into the P site. After translation has initiated, all subsequent charged tRNAs enter through the A site (including those charged with regular methionine). 

Print this record Print this record
Send to a friend Send to a friend
Show this as PDF file Show this as PDF file
Export as XML-File Export as XML-File