THE COP9 COMPLEX, A NOVEL MULTISUBUNIT NUCLEAR REGULATOR INVOLVED IN LIGHT CONTROL OF A PLANT DEVELOPMENTAL SWITCH

Arabidopsis COP9 is a component of a large protein complex that is ess ential for the light control of a developmental switch and whose confo rmation or size is modulated by light. The complex is acidic, binds he parin, and is localized within the nucleus. Biochemical purification o f the complex to near homogeneity revealed that it contains 12 distinc t subunits. One of the other subunits is COP11, mutations in which res ult in a phenotype identical to cop9 mutants. The COP9 complex may act to regulate the nuclear abundance of COP1, an established repressor o f photomorphogenic development. During the biogenesis of the COP9 comp lex, a certain degree of prior subunit association is a prerequisite f or proper nuclear translocation. Since both COP9 and COP11 have closel y related human counterparts, the COP9 complex probably represents a c onserved developmental regulator in higher eukaryotes.