Two proteins are normally found in the cytosol They are invo

Two proteins are normally found in the cytosol. They are involved in DNA double strand break repair. When DNA damage is detected, they enter the nucleus and locate on the DNA to fix it. After the process is complete, they exit the nucleus. Explain how the proteins are activated and their entry into and exit from the nucleus.

Solution

Different proteins involved in such functions may undergo activation and transport by different mechanisms. I\'ll describe the most commonly used mechanism. When DNA double strand break is detected, lets say during the cell-cycle checkpoints, the cyclin-dependent kinases phosphorylate repairing proteins, causing them to get activated. The phosphorylated, activated protein may be recognized by transporter proteins that traffick them to the nuclear compartment. During the repairing process, the phosphorylated proteins would usually lose the phosphate (such as during trade-offs for the energy required for the repair, or another accessory protein involved in repair may cause de-phosphorylation). The repair protein, devoid of its phosphate group, may then be transported out of the nucleus back into the cytosol.