In all animals, the initial events of embryogenesis are controlled by maternal 
gene products that are deposited into the developing oocyte. At some point after 
fertilization, control of embryogenesis is transferred to the zygotic genome in 
a process called the maternal-to-zygotic transition. During this time, many 
maternal RNAs are degraded and transcription of zygotic RNAs ensues. There is a 
long-standing question as to which factors regulate these events. The recent 
findings that microRNAs and Smaug mediate maternal transcript degradation have 
shed new light on this aspect of the problem. However, the transcription 
factor(s) that activate the zygotic genome remain elusive. The discovery that 
many of the early transcribed genes in Drosophila share a cis-regulatory 
heptamer motif, CAGGTAG and related sequences, collectively referred to as 
TAGteam sites raised the possibility that a dedicated transcription factor could 
interact with these sites to activate transcription. Here we report that the 
zinc-finger protein Zelda (Zld; Zinc-finger early Drosophila activator) binds 
specifically to these sites and is capable of activating transcription in 
transient transfection assays. Mutant embryos lacking zld are defective in 
cellular blastoderm formation, and fail to activate many genes essential for 
cellularization, sex determination and pattern formation. Global expression 
profiling confirmed that Zld has an important role in the activation of the 
early zygotic genome and suggests that Zld may also regulate maternal RNA 
degradation during the maternal-to-zygotic transition.