| In eukaryotes, the transcription of protein-coding genes is carried out by RNA polymerase II and general transcription factors, referred to collectively as the Pol II machinery. In activated transcription, DNA-bound transcriptional activators (activators) stimulate transcription of a gene by inducing the recruitment of the Pol II machinery to promoter DNA. Activators have been shown to interact with many components of the Pol II machinery. However, the Pol II machinery alone can not support activated transcription. Significantly, Mediator, a multi-subunit coactivator conserved from yeast to human, is required for activated transcription and has been shown to interact with many activators. This study analyzes the functional requirement for mammalian Mediator in the process of activated transcription. Specifically, two activators that function in mammalian cells, adenovirus E1A protein and mammalian mitogen-activated protein kinase-regulated Elk-1, are shown to interact with the mouse Mediator complex through the Mediator subunit Sur2. Additionally, these Mediator-activator interactions are shown to be required for E1A and phosphorylated Elk-1 to support activated transcription. Lastly, a Mediator-activator interaction is observed to be required for the ability of these activators to induce the binding of components of the Pol II machinery to promoter DNA. This suggests that the localization of Mediator to promoter DNA via an interaction with activator induces the subsequent recruitment of the Pol II machinery, resulting in the stimulation of transcription at the promoter. These findings underscore the involvement and requirement of Mediator in the process of activated transcription. |
