Given below are a few statements about nuclear transport.
A. RanGTP levels are higher in the nucleus than the cytoplasm.
B. Nuclear import receptors can shuttle between the nucleus and cytoplasm.
C. NTF2 transports RanGDP into the cytosol.
D. Export of mRNA is not directly dependent on Ran.
E. tRNA and miRNA export is mediated by exportins.

Which one of the following combinations contains all correct statements?

Correct option is C

Explanation-

Statement A -  RanGTP levels are higher in the nucleus than the cytoplasm   - CORRECT
RanGTP is generated in the nucleus via RanGEF (RCC1), while RanGAP (which hydrolyzes RanGTP to RanGDP) is in the cytoplasm. This gradient drives the directionality of nuclear transport.
Statement B - Nuclear import receptors can shuttle between the nucleus and cytoplasm   - CORRECT
Importins bind cargo in the cytoplasm, transport it into the nucleus, release the cargo upon RanGTP binding, and return to the cytoplasm.
Statement C - NTF2 transports RanGDP into the cytosol  - INCORRECT
NTF2 actually  transports RanGDP  into the nucleus, not into the cytosol. Once in the nucleus, RanGDP is converted back to RanGTP by RCC1.
Statement D -  Export of mRNA is not directly dependent on Ran   - CORRECT
mRNA export is Ran-independent. It involves NXF1/TAP-p15 heterodimer rather than classical exportins.
Statement E -  tRNA and miRNA export is mediated by exportins   - CORRECT
Exportin-t exports tRNAs. Exportin-5 exports pre-miRNAs in a RanGTP-dependent manner.

Correct Answer: Option c (A, B, D, E only)

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