The N-terminal POZ domain of GAGA mediates the formation of oligomers thatbind DNA with high affinity and specificity

The Drosophila GAGA factor self-oligomerizes both in vivo and in vitro. GAG A oligomerization depends on the presence of the N-terminal POZ domain and the formation of dimers, tetramers, and oligomers of high stoichiometry is observed in vitro. GAGA oligomers bind DNA with high affinity and specifici ty, As a consequence of its multimeric character, the interaction of GAGA w ith DNA fragments carrying several GAGA binding sites is multivalent and of higher affinity than its interaction with fragments containing single shor t sites. A single GAGA oligomer is capable of binding adjacent GAGA binding sites spaced by as many as 20 base pairs. GAGA oligomers are functionally active, being transcriptionally competent in vitro. GAG;A-dependent transcr iption activation depends strongly on the number of GAGA binding sites pres ent in the promoter. The POZ domain is not necessary for in vitro transcrip tion but, in its absence, no synergism is observed on increasing the number of binding sites contained within the promoter. These results are discusse d in view of the distribution of GAGA binding sites that, most frequently, form clusters of relatively short sites spaced by small variable distances.