The activity of E1 can be regulated at multiple levels:
Post-translational modifications: Phosphorylation and ubiquitination of E1 can modulate its activity. Protein-protein interactions: Binding to specific cofactors or inhibitors can influence E1's function. Gene expression: The transcriptional regulation of E1 genes can affect the amount of enzyme present in the cell.
This multi-layered regulation ensures that E1 activity is tightly controlled according to the cellular needs.