Elongin functions as a loading factor for Mediator at ATF6α-regulated ER stress response genes

The bZIP transcription factor ATF6 alpha is a master regulator of endo-plasmic reticulum (ER) stress response genes. In this report, we identify the multifunctional RNA polymerase II transcription factor Elongin as a cofactor for ATF6 alpha-dependent transcription activa-tion. Biochemical studies reveal that Elongin functions at least in part by facilitating ATF6 alpha-dependent loading of Mediator at the promoters and enhancers of ER stress response genes. Depletion of Elongin from cells leads to impaired transcription of ER stress response genes and to defects in the recruitment of Mediator and its CDK8 kinase subunit. Taken together, these findings bring to light a role for Elongin as a loading factor for Mediator during the ER stress response.