Why does the nuclear envelope disintegrate during prometaphase?

The disintegration of the nuclear envelope during prometaphase is primarily due to the phosphorylation of nuclear pore proteins and other proteins associated with the nuclear envelope. This phosphorylation event is crucial for the breakdown of the nuclear envelope, allowing for the proper attachment of spindle microtubules to the chromosomes.

During prometaphase, the cell prepares for chromosome segregation. As the mitotic spindle forms, it is imperative that the chromosomes are accessible, which the disintegration of the nuclear envelope facilitates. Phosphorylation alters the structural integrity of the nuclear envelope by affecting proteins that maintain its stability, including those in the nuclear lamina and nuclear pore complexes.

By making these proteins less stable, the nuclear envelope becomes fragmented, which promotes the dynamic interactions necessary for the spindle apparatus to perform its role in ensuring accurate chromosome segregation. This process ensures that the replicated chromosomes can be effectively captured by spindle fibers, leading to correct alignment and separation during subsequent phases of mitosis.