GAGA FACTOR-BINDING TO DNA VIA A SINGLE TRINUCLEOTIDE SEQUENCE ELEMENT

GAGA transcription factor (GAF) is an essential protein in Drosophila, important for the transcriptional regulation of numerous genes. GAF b inds to GA repeats in the promoters of these genes via a DNA-binding d omain containing a single zinc finger. While GAF binding sites are typ ically composed of 3.5 GA repeats, the Drosophila hsp70 gene contains much smaller elements, some of which are as little as three bases (GAG ) in length. Interestingly, the binding of GAF to more distant trinucl eotide elements is relatively strong and not appreciably affected by t he removal of larger GA arrays in the promoter, Moreover, a simple syn thetic GAG sequence is sufficient to bind GAF in vitro. Here we direct ly compare the affinity of GAF for different sequence elements by immu noprecipitation and gel mobility shin analysis, Furthermore, our measu res of the concentration of GAF in vivo indicate that it is a highly a bundant nuclear protein, prevalent enough to occupy a sizable fraction of correspondingly abundant trinucleotide sites.