Question

Cyclin B1, a key cell cycle regulatory protein in vertebrates, is mostly cytosolic before mitosis. Early in mitosis, however, the protein is phosphorylated by certain protein kinases and consequently accumulates in the nucleus. How can phosphorylation bring about nuclear accumulation of this protein?

Answer 1

Phosphorylation within the nuclear export signal interferes with the function of the signal.

Step-by-step explanation:

In biochemistry, phosphorylation is the addition of a phosphate group (PO4) to a protein or other molecule. Phosphorylation is a major player in protein regulation mechanisms, preventing protein-catalyzed reaction product from accumulating in the body causing problems.

However, in some cases phosphorylation may cause nuclear accumulation of a protein in the nucleus of the cell. An example of this is the protein shown in the question above. In this case, phosphorylation in the nuclear export signal interferes with the signal function, resulting in protein accumulation in the nucleus.