Ubiquitination

 Ubiquitination involves a small protein called Ubiquitin (Ub) attatching to target proteins, either by monoubiquitination, where there is only one molecule of Ub, or several molecules that form a chain. This chain can be used to identify proteins that are destined for protein degradation. The ubiquitination mechanism also involves different enzymes that require and rely on energy derived from ATP, which can then be used to form bonds between the Ub protein molecule and the target protein.