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Alwayssunnyinarizona t1_isi5agh wrote

You got it. They'll most often have a nuclear localization sequence - a "tag" of a short length of amino acids that tell the cell "this one goes to the nucleus."

https://en.wikipedia.org/wiki/Nuclear_localization_sequence

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Xilon-Diguus t1_isjd1lp wrote

It is also worth pointing out that we do this on purpose and can modify the proteins we insert into genomes to contain an NLS (Nuclear Localization Sequence).

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scuba_dooby_doo OP t1_isk7pbl wrote

Thank you for answering a 3am thought of this bio student! And for also answering my next question of how the cell 'knows' where to send it!

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marieterna t1_isi5ywn wrote

All translation begins in cytosol, by a cytosolic (free) ribosome. Remember, the rough endoplasmic reticulum is studded with ribosomes. A protein has a specific amino acid sequence that signals the ribosome where that protein needs to move. If that signal is reached during translation of the protein, this is called co-translational protein translocation (a mouthful, I know.) This typically pertains to proteins that are involved in cell membrane structure or proteins that need to be secreted. The ribosomes move to the RER with the incomplete protein, and feed it into the RER.

For proteins that stay inside the cell, they are shuttled to where they need to go because of the recognition of their targeting sequence. This is post-translational translocation. Specifically, for nuclear import (which is very selective), a special tag called a nuclear localization signal (NLS) is attached to the protein so it can pass through the nuclear pores.

Here’s a nice paper on this: https://www.ncbi.nlm.nih.gov/books/NBK26932/ “…histones, DNA and RNA polymerases, gene regulatory proteins, and RNA-processing proteins—are selectively imported into the nuclear compartment from the cytosol, where they are made.”

I’d love to answer any questions you may have! EDITS: Spelling, structure of paragraphs

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erublind t1_isj48qx wrote

Membrane proteins of the inner nuclear membrane (INM) was part of my research project, once upon a time. The nuclear pore complex has eight sided symmetry, with a central channel and eight peripheral routes, probably for membrane proteins. Every mitotic cycle, the nuclear membrane kind of melts into the er and is reformed around the daughter nuclei, probably directed by ranGTP gradient and proteins of the INM.

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marieterna t1_isjun7f wrote

Oh wow, that’s really interesting. Do you have any readings about that?

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scuba_dooby_doo OP t1_iskdik6 wrote

Thank you! I knew about nuclear pores and knew that they were selective so this makes sense! I'll check out the paper, thanks again 👍

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Significant-Tie-6624 t1_iu80gbe wrote

Rough endoplasmic reticulum is studded with ribosomes and synthesises the ribosomes, Golgi apparatus transports the ribosomes which synthesises proteins, and smooth endoplasmic reticulum transports the proteins to the nucleus. I think. I recently learnt this and think that's what happens

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