The mouse Grg gene encodes a 197 amino acid nuclear protein homologous to the 
amino-terminal domain of the product of the groucho (gro) gene of the Drosophila 
Enhancer of split complex. Recent work has suggested that the gro protein 
functions as a transcriptional corepressor during Drosophila development. We 
therefore examined possible roles of the mouse Grg protein in DNA binding and in 
vitro transcription. No sequence-specific DNA binding activity was detected by 
polymerase chain reaction-DNA binding site selection nor was the glutamine-rich 
Grg protein capable of acting as an activation domain in an in vivo 
transactivation assay. However, depletion of Grg protein from HeLa nuclear 
extracts inhibited the in vitro transcription activity of the extracts. We 
suggest that Grg protein may interact with components of the basal transcription 
machinery.