Characterization and Purification of Kinase Activities against Arabidopsis COP9 Signalosome Subunit 7

摘要

The COP9 signalosome(CSN)is a multisubunit protein complex that intersects the ubiquitin(Ub)-proteasome pathway at several junctions.The CSN associates with several protein kinases that target key regulatory proteins that themselves are targets for Ub-dependent degradation,and several subunits themselves are phosphoproteins.We previously reported that Arabidopsis CSN7 is a phosphoprotein.To identify the kinases responsible for CSN7 phosphorylation,we biochemically purified CSN7-kinsae activities from cauliflower through a four-step purification procedure that resulted in a ca.300-fold enrichment.One of these activities is Ca~(2+)dependent,while the second is not.Peptide fingerprint analysis of the purified proteins identified three putative CSN7 kinases.