The enzymes involved in ubiquitinylation of cell-cycle proteins are

1. $\text{E}_{1}$ and $\text{E}_{2}$ Only
2. $\text{E}_{1}$ and $\text{E}_{3}$ Only
3. $\text{E}_{1}$ and $\text{E}_{4}$ Only
4. $\text{E}_{1}$, $\text{E}_{2}$ and $\text{E}_{3}$