Question

the protein xpot transports all tRNAs out of the nucelus so that they can be aminoacylated in the cytosol.

a) What tRNA structural feature is Xpot likely to recognize?
b) Why might it be beneficial for aminoacylation to occur in the cytosol?

Answer 1

a ) Aminoacylation is the process of adding an aminoacyl group to a compound. It produces a tRNA molecule with its CCA 3' end covalently linked to an amino acid.

Each tRNA is aminoacylated with a specific amino acid by an aminoacyl tRNA synthetase. There is normally a single aminoacyl tRNA synthetase for each amino acid, despite the fact that there can be more than one tRNA, and more than one anticodon, for an amino acid. Recognition of the appropriate tRNA by the synthetases is not mediated solely by the anticodon, and the acceptor stem often plays a prominent role.

Reaction:

1. amino acid + ATP → aminoacyl-AMP + PPi
2. aminoacyl-AMP + tRNA → aminoacyl-tRNA + AMP

In some of the aminoacyl tRNA synthetases, the cavity that holds the amino acid can be mutated and modified to carry unnatural amino acids

b ) In eukaryotic cells most RNAs are transcribed in the nucleus but perform their cellular functions in the cytosol. Export of RNA from the nucleus occurs across nuclear pores, channels connecting the nuclear and cytosolic compartments. Transport of macromolecules across the nuclear boundary requires a functional small GTPase, Ran, its regulators, and members of the family of Ran-binding proteins known as importins and exportins. It has been proposed that RanGTP, primarily located in the nucleus, and RanGDP, primarily located in the cytosol.