91Ó°ÊÓ

In this exercise, we investigated three different levels of gene expression regulation: (a) transcription initiation, (b) protein stability, and (c) protein posttranslational modification. At the level of transcription initiation, we identified transcription factors, such as the TATA-binding protein, as regulators that bind to specific DNA sequences enabling RNA polymerase to initiate transcription. At the level of protein stability, the ubiquitin-proteasome system is an example of a regulatory process involving ubiquitin tagging of target proteins for degradation by the proteasome, thus controlling protein abundance in a cell. Lastly, at the level of protein posttranslational modification, protein phosphorylation serves as a regulator through the addition of phosphate groups to proteins by kinase enzymes, like Protein Kinase A, which can alter various aspects of the target protein's function.