Human PC4 is a non-TAF transcription coactivator that mediates activator-dependent transcription by RNA polymerase II in vitro through most tested activators (1, 2). Phosphorylation negatively regulates the function of coactivator PC4. Mutational and mass spectroscopy studies suggest that the in vitro and in vivo hyperphosphorylation of PC4 is mediated by casein kinase II and is restricted to the the N-terminal serine–rich region. Phosphorylation of PC4 by casein kinase II inhibits the p300-mediated acetylation (3, 4). The wild-type PC4, but not the kinase inhibitory-deficient mutant of PC4 (serine mutations), represses specific transcription in vivo (5). Recombinant PC4 protein (serine mutations, 127 amino acids) is isolated from an E. coli strain that carries the coding sequence of human PC4 under the control of T7 promoter and purified by conventional chromatography. Recombinant PC4 has been utilized for in vitro function studies, including transcription, DNA replication, in vitro phosphorylation, gel mobility shift assay, protein-protein interactions and as a substrate for in vitro acetylation. Protein is greater than 95% homogeneous based on SDS-PAGE analysis. 1 unit equals 1 nanogram of purified protein. 1 unit is sufficient for a gel mobility shift assay in a 20 µl reaction; 20 units are sufficient for reconstituted transcription assay and 100 units are sufficient for a protein-protein interaction assay. variable in different lots 1x dilution buffer A: 20 mM Tris-Cl (pH 8.0), 20% Glycerol, 100 mM KCl, 1 mM DTT and 0.2 mM EDTA
References
1. Ge, H. et al., (1994) Cell 78, 513-523 2. Kretzschmar, M. et al., (1994) Cell 78, 525-534 3. Ge, H. et al., (1994) Proc. Natl. Acad. Sci. USA 91, 12691-12695 4. Kumar, BR. et al., (2001) J. Biol. Chem. 276, 16804-1689 5. Schang, LM. et al., (2000) J. Biol. Chem. 275, 6071-6074
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