CCG1/TAFII250, the largest subunit of theTFIID complex, is mutated in ts cell cycle mutants of BHK21 cells, ts13 and tsBN462, which have a promoter-selective transcriptional defect. A series of deletion mutants of CCG1 cDNA were prepared and transfected into these mutants, in order to identify functional domains of CCG1 required for the complementation of ts 13/BN462 mutation. We determined the minimum size of CCG1: CCG1ME, essential for complementing the ts mutation, which possessed one proline cluster, an HMG1-like domain, and a nuclear localization signal, but which lacked the bromo domains and the acidic phosphorylation sites for casein kinase II common to transcriptional activators. It encodes a protein of 140 kDa. These characteristics of CCG1ME correspond to yeast TAFII145, the yeast homolog of human TAFII250. CCG1ME bound to TBP, creating its own TFIID complex different from that of the endogenous mutated CCG1 in ts+ transformants of tsBN462 cells.
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