Nucleo-Cytoplasmic Exchange

ID #2436

Aside from ribosomal proteins, Which molecules have an NLS and an NES? I see that a nuclear transport receptor also has both a NES and a NLS. But I am a bit confused as to what the mRNA binds to in order to be exported out of the nucleus. I tried to phrase it like this: "In order for a processed mRNA molecule to be transported out of the nucleus, it is coated by proteins, which have a NES, and the proteins are then bound to exportin. One of these proteins is a nuclear transport receptor, which has both an NLS and an NES because it needs to get returned to the nucleus." Is this correct?

A variety of proteins have NLS or NES as signals- it really depends on a protein's function or where they need to work. The "nuclear transport receptor" or the "exporter complex" from one of the figures in lecture 25 you are describing, is really just a protein that exports mRNA from the nucleus to the cytoplasm for translation (so a shuttle protein). An mRNA ready to be exported is coated with proteins- at least one of them must have a NES so that the entire complex can be recognized by an exportin and can leave the nucleus. (Not every protein needs an NES- only one NES is technically necessary for the entire complex to leave the nucleus. Others may have one as well). These shuttle proteins will need their own NLS signals to re-enter the nucleus following export of the mRNA, unless they find a protein partner that has an NLS. They will then be transported back into the nucleus with the help of importin molecules. 

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