A C-elegans mediator protein confers regulatory selectivity on lineage-specific expression of a transcription factor gene

The Caenorhabditis elegans caudal homolog, pal-1, is required for neurogene sis in the male tail. We show that expression of pal-1 in the postembryonic neuroblast cell V6 can be initiated by two alternate pathways. One pathway , acting in wild type, requires a regulatory element in the fifth pal-1 int ron. The other pathway, independent of this element, is normally repressed by the newly identified gene sop-1, which encodes a homolog of the mammalia n Mediator complex protein TRAP230. In sop-1 mutants, pal-1 is activated by a pathway that is stimulated by bar-1/beta-catenin, a component of the Wnt signal transduction pathway. The results support a physiological role of t he Mediator complex in conveying regulatory signals to the transcriptional apparatus.