What can be inferred about the size of proteins that require transport into the nucleus?

Proteins that require transport into the nucleus are typically larger and cannot diffuse freely through the nuclear pore complex. The nuclear envelope has specialized structures that regulate the movement of molecules in and out of the nucleus, and these structures are more permeable to smaller molecules, such as ions or small signaling molecules. Larger proteins, especially those that are over about 40 kDa, require active transport mechanisms. This transport often involves specific nuclear localization signals (NLS) that are recognized by transport receptors, allowing the larger proteins to be shuttled into the nucleus.

Because the nuclear pore complex has a size exclusion limit, larger proteins cannot passively diffuse through the nuclear membrane. Instead, they need the assistance of nuclear transport receptors that facilitate their movement. This is why the correct inference is that these proteins are typically larger and require a more active mode of transport to enter the nucleus.