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 three embryonic head segments. It encodes a zinc-finger-type transcription factor expressed in the corresponding head segment anlagen in the blastoderm stage embryo. The DNA-binding properties of the btd protein (BTD) are indistinguishable 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-associated factors and support in vitro transcription activation through these contacts. Transgene expression of BTD results in the rescue of the head segments that fail to develop in btd mutant embryos, whereas Sp1 or Sp1 containing the zinc finger region of BTD rescues mandibular segment development. The results suggest that BTD contains functional domains other than an equivalent DNA-binding region and interaction sites of the TATA box-binding protein-associated factors, which are necessary to establish head segments that fail to develop in response to Sp1.

果蝇（Drosophila）钮头基因（buttonhead，btd）是三个胚胎头部体节建立所必需的。该基因编码一种锌指型转录因子（zinc-finger-type transcription factor），在囊胚期胚胎（blastoderm stage embryo）的相应头部体节原基中表达。btd蛋白（BTD）的DNA结合特性与人类转录因子Sp1完全一致。此外，BTD与Sp1均可通过结合相同的DNA靶位点，在转染的培养细胞中激活转录。本研究证实，BTD与Sp1可与同一组TATA盒结合蛋白相关因子（TATA box-binding protein-associated factors）发生功能性互作，并通过这些相互作用介导体外转录激活。通过转基因表达BTD，可挽救btd突变体胚胎中无法正常发育的头部体节；而单独表达Sp1，或携带BTD锌指结构域（zinc finger region）的Sp1变体，则仅能挽救下颌体节的发育。上述结果表明，除了保守的DNA结合区域与TATA盒结合蛋白相关因子互作位点外，BTD还拥有其他功能结构域，这些结构域对于建立Sp1无法介导其发育的头部体节是必需的。