Figure 1: The nuclear envelope.

The nuclear envelope is composed of two membranes (in blue; the inner nuclear membrane (INM) and outer nuclear membrane (ONM)), nuclear pore complexes (NPC; in purple) and a nuclear lamina (in red). Not shown are many inner and outer nuclear membrane proteins that are also part of the nuclear envelope. The ONM is continues with the ER, a single tube of which is shown connected to the nuclear envelope. Green arrows: indicate a hypothetical flow of membrane components from the ER to the nuclear membranes. Orange arrows: indicate a hypothetical force applied on the nuclear membranes when nuclear protein concentration increases.