Functional Assignment among Chromatin Chaperones

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The aim of this study is to systematically identify chromatin chaperones involved in chromatin remodeling and to clarify the regulatory mechanism of their activities and the functional assignment among them. We have identified Template Activating Facor (TAF)-III in addition to previously identified TAF-I and TAF-II/Nucleosome Assembly Protein-I by reconstitution and dissection of cell free replication and transcription systems with the adenovirus DNA complexed with viral basic core proteins astemplate. TAF-III was shown identical with nucleophosmin/B23. Analyzes with mutated proteins revealed that the highly acidic amino region in three proteins is essential for their chromatin remodeling activity. We proposed the term "acidic molecular chaperone" for these proteins. Each TAF-I or TAF-III consists of two subtypes, one of which has much less activity than the other. We showed the possibility that the ratio of these two subtypes in a cell is involved in the activity level. The chromatin … More remodeling activity of TAF-I and TAF-III was phosphorylated and markedly reduced : during the mitotic phase. We showed that phosphorylation by a mitotic-specific protein kinase including cyclin B/cdc2 negatively regulates their chromatin remodeling activity. It was indicated that TAF-I and TAF-III exist in nucleus and nucleolus, respectively, while TAF-II was found a nucleocytoplasmic shuttling protein. TAF-I was involved in not only the adenovirus chromatin but also the cellular type chromatin reconstituted with purified histones and plasmid DNA. Genetic experiments using yeast cells indicated that Shuttling but not nuclear localization is important for mitotic progression. Chromatin immunoprecipitation assays showed that TAF-III is associated with the ribosome DNA region. Of interest, is that by functuional analysis of influenza virus ribonucleoproteins, we identified RAF (RNA polymerase Activating Factor)-1 and RAF-2p48/NPI 5/BAT-1/UAP56 as a family member of the acidic molecular chaperone. Thus, it is suggested that proteins categorized into this family involves in function regulation of not only DNA-protein complexes but also RNA-protein complexes. Less