Describe the transport of proteins across nuclear membrane?

Proteins are transported across the nuclear membrane through a process called nuclear import and export.

Nuclear import involves the movement of proteins from the cytoplasm into the nucleus. This process is mediated by nuclear localization signals (NLS) on the protein, which are recognized by importins. Importins bind to the NLS and facilitate the transport of the protein through nuclear pore complexes in the nuclear membrane. Once inside the nucleus, the protein is released from the importin and can carry out its function.

Nuclear export, on the other hand, involves the movement of proteins from the nucleus to the cytoplasm. This process is mediated by nuclear export signals (NES) on the protein, which are recognized by exportins. Exportins bind to the NES and facilitate the transport of the protein through nuclear pore complexes in the nuclear membrane. Once in the cytoplasm, the protein is released from the exportin and can carry out its function.

Overall, the transport of proteins across the nuclear membrane is a highly regulated process that ensures the proper localization of proteins within the cell.