Drosophila head segmentation factor Buttonhead interacts with the same TATA box-binding protein-associated factors and in vivo DNA targets as human Sp1 but executes a different biological program

The Drosophila gene buttonhead (btd) is required for the establishment of t hree embryonic head segments. It encodes a zinc-finger-type transcription f actor expressed in the corresponding head segment anlagen in the blastoderm stage embryo. The DNA-binding properties of the btd protein (BTD) are indi stinguishable from the human transcription factor Sp1. Furthermore, BTD and Sp1 are capable of activating transcription in transfected cultured cells through interaction with the same DNA target sites. Herein we show that BTD and Sp1 functionally interact with the same TATA box-binding protein-assoc iated factors and support in vitro transcription activation through these c ontacts. Transgene expression of BTD results in the rescue of the head segm ents that fail to develop in btd mutant embryos, whereas Sp1 or Sp1 contain ing the zinc finger region of BTD rescues mandibular segment development. T he results suggest that BTD contains functional domains other than an equiv alent DNA-binding region and interaction sites of the TATA box-binding prot ein-associated factors, which are necessary to establish head segments that fail to develop in response to Sp1.