What structure regulates the entry and exit of proteins and RNA through the nuclear envelope?

The structure responsible for regulating the entry and exit of proteins and RNA through the nuclear envelope is the pore complex. The nuclear pore complex is a large protein assembly that spans the nuclear envelope, providing gateways through which molecules can move. This structure is crucial for maintaining the distinct environments of the nucleus and the cytoplasm; it allows the selective transport of molecules—such as RNA being exported from the nucleus and proteins being imported into it—while preventing the free passage of larger macromolecules.

The nuclear pore complex is composed of multiple proteins called nucleoporins, which form a complex configuration that can change shape to allow substances to pass through. Small molecules can diffuse freely, but larger molecules require active transport mechanisms facilitated by specific transport proteins that recognize signal sequences.

The other options, while related to the nuclear structure, do not serve the same function as the pore complex. The nuclear lamina provides structural support to the nucleus and helps organize chromatin, while the nuclear matrix is a network that also helps organize nuclear contents. Cytoplasmic filaments play a role in providing structural support outside the nucleus and facilitating interactions in the cytoplasm, but they don't directly regulate nucleocytoplasmic transport.