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Broad Requirement for the Mediator Subunit RGR-1 for Transcription in the Caenorhabditis elegans Embryo*

The Mediator-related transcription co-factors integrate positive and negative inputs and recruit and activate the RNA polymerase II complex. To understand the role of Mediator during transcription, it is important to identify Mediator subunits that are essential for its functions. In the yeast Mediator, the conserved component Rgr1 is associated with multiple subunits that are required for specific activation or repression events. Yeast rgr1 is essential for viability, for certain repression mechanisms, and for activation of heat shock genes, but it is not known whetherrgr1 is generally important for transcription. Here we have performed the first analysis of rgr-1 function in a metazoan. We found that in the developing Caenorhabditis elegans embryo rgr-1 is broadly required for transcription and for phosphorylation of both Ser-2 and Ser-5 of the RNA polymerase II C-terminal domain repeat. We conclude that RGR-1 fulfills a critical Mediator function that is broadly essential for metazoan mRNA transcription and that RGR-1 may be required at an early recruitment or initiation step.