Maternally contributed mRNAs and proteins control the initial stages of 
development following fertilization. During this time, most of the zygotic 
genome remains transcriptionally silent. The initiation of widespread zygotic 
transcription is coordinated with the degradation of maternally provided mRNAs 
at the maternal-to-zygotic transition (MZT). While most of the genome is 
silenced prior to the MZT, a small subset of zygotic genes essential for the 
future development of the organism is transcribed. Previous work in our 
laboratory and others identified the TAGteam element, a set of related 
heptameric DNA-sequences in the promoters of many early-expressed Drosophila 
genes required to drive their unusually early transcription. To understand how 
this unique subset of genes is regulated, we identified a TAGteam-binding factor 
Grainyhead (Grh). We demonstrated that Grh and the previously characterized 
transcriptional activator Zelda (Zld) bind to different TAGteam sequences with 
varying affinities, and that Grh competes with Zld for TAGteam occupancy. 
Moreover, overexpression of Grh in the early embryo causes defects in cell 
division, phenocopying Zld depletion. Our findings indicate that during early 
embryonic development the precise timing of gene expression is regulated by both 
the sequence of the TAGteam elements in the promoter and the relative levels of 
the transcription factors Grh and Zld.