Transcriptional repression by the Caenorhabditis elegans germ-line proteinPIE-1

In the early Caenorhabditis elegans embryo, maternally expressed PIE-1 prot ein is required in germ-line blastomeres to inhibit somatic differentiation , maintain an absence of mRNA transcription, and block phosphorylation of t he RNA polymerase II large subunit (Pol II) carboxy-terminal domain (CTD). We have determined that PIE-1 can function as a transcriptional repressor i n cell culture assays. By fusing PIE-1 sequences to the yeast GAL4 DNA-bind ing domain, we have identified a PIE-1 repression domain that appears to in hibit the transcriptional machinery directly. A sequence element that is re quired for this repressor activity is similar to the Pol II CTD heptapeptid e repeat, suggesting that the PIE-I repression domain might target a protei n complex that can bind the CTD. An alteration of this sequence element tha t blocks repression also impairs the ability of a transgene to rescue a pie -1 mutation, suggesting that this repressor activity may be important for P IE-1 function in vivo.