The RING finger motif of photomorphogenic repressor COP1 specifically interacts with the RING-H2 motif of a novel Arabidopsis protein.
The constitutive photomorphogenic 1 ( COP1) protein of Arabidopsis functions as a molecular switch for the seedling developmental fates: photomorphogenesis under light conditions and skotomorphogenesis in darkness. The COP1 protein contains a cysteine-rich zinc-binding RING finger motif found in diverse groups of regulatory proteins. To understand the role of the COP1 RING finger in mediating protein-protein interaction, we have performed a yeast two-hybrid screen and isolated a novel protein with a RING-H2 motif, a variant type of the RING finger. This protein, designated COP1 Interacting Protein 8 (CIP8), is encoded by a single copy gene and localized to cytosol in a transient assay. In addition to the RING-H2 motif, the predicted protein has a C4 zinc finger, an acidic region, a glycine-rich cluster, and a serine-rich cluster. The COP1 RING finger and the CIP8 RING-H2 domains are sufficient for their interaction with each other both in vitro and in yeast, whereas neither motif displayed significant self-association. Moreover, site-directed mutagenesis studies demonstrated that the expected zinc-binding ligands of the RING finger and RING-H2 fingers are essential for their interaction. Our findings indicate that the RING finger motif, in this case, serves as autonomous protein-protein interaction domain. The allele specific effect of cop1 mutations on the CIP8 protein accumulation in seedlings indicates that its stability in vivo is dependent on the COP1 protein.[1]References
- The RING finger motif of photomorphogenic repressor COP1 specifically interacts with the RING-H2 motif of a novel Arabidopsis protein. Torii, K.U., Stoop-Myer, C.D., Okamoto, H., Coleman, J.E., Matsui, M., Deng, X.W. J. Biol. Chem. (1999) [Pubmed]
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