Enzymatic Activities of TFIID

The TAF1 component of TFIID possesses multiple enzymatic activities that are able to covalently modify histone tails and thus facilitate the reconfiguration of the chromatin structure in order to overcome nucleosome-mediated repression. TAF1 is known to function as an acetyltransferase in acetylating histones H3 and H4 (Mizzen et al., 1996), as a kinase in phosphorylating histone H2B (Maile et al., 2004), and as a histone-specific ubiquitin-activating conjugating enzyme in mediating...

Sk

Fig. 14.6 Cellular P-TEFb heterodimers exist in two distinct states that are kept in a functional equilibrium. In HeLa cell, about half of nuclear P-TEFb are sequestered in the inactive 7SK HEXIM1 P-TEFb snRNP, where HEXIM1 binds to and inhibits P-TEFb's kinase activity through a 7SK-dependent process. The 7SK snRNP is unable to phosphorylate Pol II or associate with a promoter. Treatment of cells with certain stress-inducing agents or hypertrophic signals can cause rapidly dissociation of 7SK...

Hat Hdac and Histone Acetylationa More Complicated Picture

Although it is generally thought that histone deacetylation causes gene repression, several studies now reveal a much more complex picture. For example, in a genome-wide CHIP analysis in yeast, it was revealed that the recruitment of the histone deacetylase HOS2 to the coding region of specific genes is correlated with gene activation, rather than repression (Wang et al., 2002). Since there is concurrent deacetylation of histone H3 and H4, these observations demonstrate that histone...

Regulation by PIAS Proteins

The activity of STAT proteins can be regulated by the protein inhibitor of activated STAT (PIAS) family (Shuai and Liu, 2003). The involvement of PIAS proteins in the regulation of STATs was first revealed through yeast two-hybrid assays. Using STATip as the bait, PIAS1 was isolated as a STAT 1-interacting protein (Chung et al., 1997 Liu et al., 1998). Subsequent cDNA library screening and sequence analysis have identified additional members of the PIAS family. The mammalian PIAS family...

Class I HDACs

The HDAC domains of class I are homologous to the yeast protein Rpd3 (Taunton et al., 1996). In humans, the class I HDACs consist of HDAC1, 2, 3, and 8. HDAC 11 is also nominally a class I HDAC, but it is more divergent from the others and has some similarities with class II HDACs (Gao et al., 2002). Class I HDACs are significantly smaller than class II HDACs and are predominantly nuclear proteins, although a recent report has indicated that HDAC8 may be cytosolic in smooth muscle cells...