Ubiquitous expression and embryonic requirement for RNA polymerase II coactivator subunit Srb7 in mice

Mammalian RNA polymerase II complexes and coactivators containing homologs of yeast Srb/Med proteins have been isolated recently from tissue culture c ells. The yeast Srb/Med complex is involved in global gene expression and i s essential, but it is not yet known if its mammalian counterparts are broa dly expressed in tissues or if they are essential. We have isolated the mur ine gene encoding Srb7, an Srb/Med complex protein whose sequence and funct ion is highly conserved between yeast and humans. The mouse Srb7 gene is si ngle copy, and Northern analysis showed that it is expressed in all tissues examined. Disruption of the gene in embryonic stem cells revealed that it is essential for cell viability and murine embryonic development. These res ults, together with evidence that murine Srb7 is associated exclusively wit h high molecular weight forms of RNA polymerase II in extracts, suggest tha t Srb7-containing polymerase complexes occur in most tissues and have essen tial roles in expression of protein coding genes.