The Grg gene encodes a 197-amino-acid protein homologous to the amino-terminal 
domain of the product of the groucho gene of the Drosophila Enhancer of split 
complex. We describe here the genomic organization of the mouse Grg gene. It 
spans approximately 7 kb on chromosome 10 and consists of seven exons. The 3' 
region of the Grg gene contains two functional polyadenylation sites that give 
rise to two transcripts that are differentially expressed among adult mouse 
tissues. The promoter region is very GC rich and lacks TATA box and "initiator" 
sequences. Primer extension analysis and ribonuclease protection assays show 
that Grg has a major transcription start site situated down-stream of putative 
binding motifs for the transcription factors Sp1, E2A, and PuF.