(D) A hypothesized model for inhibition of COP1 nuclear export by TRIB1 through NES masking. In this model, binding of the PSL to the WD40 domain stabilizes a conformation in which the NES, located in the distal putative coiled coil domain, is exposed. This could be achieved by an effective reduction of the distance between the WD40 domain and the putative coiled coil domain, resulting from PSL binding. Loss of this proximity upon TRIB1 binding could then induce a conformational change in the coiled coil domain that results in NES masking. 