Question

Describe the activation cycle of the RAN-GTPase. Identify the factor(s) responsible for the directionality of transport across the nuclear envelope.  

Answer 1

RAN-GTPase mediate import and export of Rna or proteins in nucleus through nuclear pores.

RAN is small protein which is soluble and mobile throughout cell and when it is bound to GTP during active form and inactivate form RAN-GDP.

Key proteins activate RAN

RCC1 - RAN regulator (It is a major RAN guanine nucleotide exchange factor)

RANGap - RAN GTPase activating Protein

In cytoplasm RAN interact with RANGap, after that interact with RCC1 in nucleus which is associated by chromatin. This creates RAN-GTP gradient active Ran increase in nucleus.

Karyopherins are the protein which helps larger protein to pass across the Nuclear pore complex. They classified according to thier function Importin (import protein into nucleus) and exportin(export outside nucleus).

Protein which contains NLS(nuclear localisation sequence) tag binds to Importin protein form complex and diffuse into nucleus through nuclear pore after that RAN GTPase bind with importin and dissociate complex after that importin export in cytoplasm.

During export of protein RANGTPase bind with exportin and protein which export or contains Nuclear export sequence and form complex with protein and export in cytoplasm through nuclear pore.