What is the function of E3 in ubiquitin modification?

The function of E3 in ubiquitin modification primarily involves recognizing and binding to specific substrate proteins that contain degradation signals. E3 ligases play a critical role in the ubiquitin-proteasome pathway by facilitating the transfer of ubiquitin from an E2 conjugating enzyme to the substrate. The specificity of E3 ligases is crucial, as they ensure that only proteins destined for degradation are tagged with ubiquitin. By binding to these specific degradation sequences within the substrate proteins, E3 ligases dictate which proteins are marked for destruction, thereby regulating various cellular processes.

In contrast, the other options describe functions that do not accurately represent the role of E3 in the ubiquitin modification process. Detoxifying modified proteins, conjugating ubiquitin directly, and recycling ubiquitin are functions associated with other components of the ubiquitin pathway or different cellular processes altogether.