The E. coli SSB is a tetramer; eukaryotic SSB (also known as RPA) is a trimer.

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#Unit 2. Cellular Organization

An NPC is made up of many copies of some 30 different proteins called nucleoporins.

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#Unit 2. Cellular Organization

Eight approximately 100-nm long filaments extend into the nucleoplasm with the distal ends of these filaments joined by a terminal ring, forming a structure called the nuclear basket.

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#Unit 2. Cellular Organization

The nucleoporins are of three types: 

a. Structural nucleoporins

b. Membrane nucleoporins

c. FG-nucleoporins

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#Unit 2. Cellular Organization

A set of seven structural nucleoporins forms a Y-shaped structure about the size of the ribosome, known as the Y complex.

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#Unit 2. Cellular Organization

A structural motif repeated several times within the Y-complex is closely related to a structure found in the COPII proteins that drive the formation of coated vesicles within cells.

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#Unit 2. Cellular Organization

Nucleoporin

Large group of proteins that make up the nuclear pore complex. one class (FG-nucleoporins) participates in nuclear import and export.