The inhibitor protein Ikappa-B normally keeps the transcription factor NF-kappa-B out of the nucleus. What event releases NF-kappa-B so it can enter the nucleus and start transcription?

1. The inhibitor Iκ-B binds to the regulatory protein NF-κB, and while bound, the complex cannot enter the nucleus. 2. PKC phosphorylates Iκ-B. 3. Once phosphorylated, Iκ-B can no longer bind NF-κB. 4. Released from Iκ-B, NF-κB, a transcription factor, can enter the nucleus and initiate RNA transcription. 5. The effect of this phosphorylation is to inactivate an inhibitor and thereby activate transcription, the opposite of directly activating NF-κB itself. 6. The option describing Iκ-B degradation by a phosphatase misidentifies the enzyme and the mechanism, since phosphorylation by PKC, not degradation by a phosphatase, is the mechanism described. 7. The option that phosphorylates NF-κB while it is still bound to Iκ-B misplaces which protein PKC actually modifies. _Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 9 "Cell Communication", section 9.3 | Response to the Signal_