A novel mediator between activator proteins and the RNA polymerase II transcription apparatus

“Protein was determined by the method of Bradford (1976) , using bovine serum albumin as a standard, and assays of P-galactosidase activity were performed as previously described (Miller, 1972; Guarente, 1983).”

“Assays of BGaiactosidase Activity in Vivo Plasmid DNAs were introduced into Saccharomyces cerevisiae strain 5C (a his3-A200 ura3-52) by a lithium acetate transformation procedure (ito et al., 1983).”

“…GAL4-VP16, comprising the DNA binding domain (amino acids 1-147) of GAL4 fused to the activation domain (carboxy-terminal 78 amino acids) of VP16 (Sadowski et al., 1988), and a yeast factor whose binding site is a thymidine-rich sequence from upstream of the DED7 gene (T-rich binding factor; Lue…”

“Protein was determined by the method of Bradford (1976), using bovine serum albumin as a standard, and assays of P-galactosidase activity were performed as previously described (Miller, 1972; Guarente, 1983).”

“One line of evidence comes from alterations in the DNAase I footprint of partially purified HeLa TFIID on the adenovirus major late and E4 promoters caused by activator protein binding (Sawadogo and Roeder, 1985b; Horikoshi et al., 1988a, 1988b).”

“For example, herpes viral protein 16 (VP16), an activator of immediate early gene expression in herpes virus-infected cells, causes a severalfold reduction in the level of transcription of an unrelated gene (Triezenberg et al., 1988).”

“A single copy plasmid for expression of GAL4VP16 from the ADH7 plromoter, pCEN4:G4VPlG, was created by the insertion of the Kpnl fragment containing CEN4 sequences from pCZA into the unique Xbal site of pMA424 (gift of J. Ma and M. Ptashne; Ma and Ptashne, 1987) by blunt end ligation, leaving the 2pm origin intact but…”

“Similarly, high levels of the activator GAL4 in yeast cells diminish expression of genes lacking GAL4 binding sites as much as 5fold (Gill and Ptashne, 1988).”

“In the case of the vertebrate estrogen, progesterone, and glucocorticoid receptors, which activate responsive genes in the presence of hormone, various pairwise combinations of both transfected and endogenous receptor genes exhibit interference in a hormone-dependent fashion (Meyer et al., 1989).”

“A similar inhibition of activation by the GRFI binding EN07 UAS was observed.”

“In 1990 and 1991, Ray and Peter produced evidence for an additional factor required for this communication in a still crude yeast system.(17,18) This additional factor, which we referred to as Mediator, proved elusive.”

“…multi-subunit RNA polymerase II-associated transcriptional regulator, coordinates various aspects of transcription and acts as a docking site for nuclear machinery (An and Mou, 2013; Buendía-Monreal and Gillmor, 2016; Conaway and Con-away, 2011; Kelleher et al., 1990; Samanta and Thakur, 2015a).”

“Mediator complex was first discovered in yeast as a co-activator of transcription [8 – 10].”

“…as TBP or TFIIB (Choy and Green 1993; Klein and Struhl 1994) and indirect interactions via proteins that serve as co-activators (Berger et al. 1990; Kelleher et al. 1990; Flanagan et al. 1991; Chiang et al. 1993, Kim et al. 1994, Lefstin et al. 1994) mediate ordered assembly of a productive…”

“The Mediator complex was originally isolated in yeast Saccharomyces cerevisiae as a component of the basal transcription apparatus necessary for the transcriptional initiation by RNA Polymerase II (Pol II) [15].”

“The signal pathway integration not only occurs at the level of transcriptional regulation and protein posttranslational modification such as phosphorylation and ubiquitination, but also includes the transcription initiation through the mediator complex and RNA Polymerase II[28,29].”

“The discovery of Mediator began with the observation that two transcriptional activators could interfere with each other’s function invitro, even though theydidnotbind to the same promoter (Kelleher et al., 1990).”

“Med23 (also known as Crsp3), a subunit of the mediator complex which acts as a transcriptional coactivator for RNA polymerase II (43,44), shows a positive correlation with AHP amplitude (Fig 7D).”

“complex and transcriptional initiation by RNA polymerase II (192,193).”

“Kornberg and colleagues first identified Mediator in yeast in the 1990s and revealed that this complex is capable of relieving competition between activators for a common target [7].”

“11 To investigate whether the mutant’s impairment in pheromone perception is due to malformed antennae or a direct regulation of genes involved in pheromone sensing, we focused on its downregulated genes in the BmMed6 mutant.”

“The Mediator is a group of proteins that we discovered in [3] and it is an important part of the gene regulation mechanism: it processes all the regulatory information and delivers it to the RNA polymerase to control the decision of whether to transcribe a certain gene.”

“Published studies indicated that the ‘core Mediator’ serves as a 75 bridge between DNA-binding transcription factors (TFs), Pol II as well as other components 76 in the transcription machinery, which collectively plays a crucial role in transcriptional 77 activation (7-10).”

“Amongst these were several components of the Mediator complex, a multiprotein complex functioning as a transcriptional coactivator for RNA Polymerase II (highlighted in red) (19,20).”

“One key regulator of transcription is Mediator, a multiprotein complex conserved from yeast to plants to animals, which was initially identified based on its requirement for transcription of virtually all protein-coding genes (Kelleher et al., 1990; Flanagan et al., 1991; Bourbon, 2008).”

“In vitro, purified TATA-binding protein (TBP) is incapable of restoring transactivation in a cell extract that lacks TFIID activity but depends on TBPassociated proteins (14, 16, 21, 30).”

“Med23 (also known as Crsp3), a subunit of the mediator complex which acts as a transcriptional coactivator for RNA polymerase II (Kelleher et al., 1990; Ryu et al., 1999), shows a positive correlation with AHP amplitude (Figure 3.”

“The search for a “mediator” protein began when the observation was made that GTFs and RNAPII could support basal levels of transcription in vitro however they were unresponsive to transactivators (Flanagan et al., 1991; Kelleher et al., 1990).”

“The multisubunit Mediator complex functions as both a coactivator and corepressor and recruits RNA polymerase II to the promoter of activated genes (Kelleher et al., 1990; Flanagan et al., 1991).”

“The yeast Mediator complex and mammalian homologues thereof (Flanagan et al., 1991; Kelleher et al., 1990; Park et al., 2001) have gained acceptance as an important interface linking transcriptional activators to RNA pol II (Kornberg, 1999).”