Figure 9.

A Proposed Model Showing How CSU1 Regulates COP1.

In the dark, COP1 ubiquitinates downstream substrates, such as HY5, for degradation in order to repress photomorphogenesis. To maintain COP1 homeostasis, CSU1 targets COP1 for ubiquitination and degradation. In addition, CSU1 negatively regulates SPA1. In the light, COP1 is exported from the nucleus to the cytoplasm, whereas CSU1 still localizes in the nucleus. u, ubiquitin; ub, ubiquitination. Solid and dotted lines denote direct and indirect regulation, respectively.