The location, modification, and function of the fushi tarazu protein during Drosophila embryogenesis

The fushi tarazu (ftz) protein of Drosophila is required during embryogenesis for the process of body segmentation. In order to study the biochemical properties of the ftz protein, ftz cDNA was expressed in E. coli, and the protein purified to homogeneity. Polyclonal antibodies raised against the purified protein were used to localize and quantitate the protein during embryogenesis. Three temporally and spatially distinct phases of expression were observed, which include a previously undetected period later in embryogenesis. During this last phase, the protein is localized in the developing hindgut. Analysis of embryonic ftz protein on Western blots permitted us to approximate the number of protein molecules per nucleus. During the blastoderm phase of development, when ftz protein is most abundant, we calculate that there are 15,000 molecules of protein per ftz-expressing nucleus. Since embryonic ftz protein migrates more slowly on SDS polyacrylamide gels than protein expressed either in E. coli, or in vitro in a reticulocyte lysate system, it is apparently modified in the embryo. Two-dimensional gel electrophoresis followed by Western blotting resolves the protein into a series of isoforms which have variable charge and electrophoretic mobility. When compared in its ability to bind DNA in a sequence-specific manner, it was also found that ftz protein partially purified from embryos binds with greater specificity than its bacterially expressed counterpart. In this paper, we demonstrate that embryonic ftz protein binds to a specific region within the ftz enhancer element. The potential relationship between these observations is discussed.