Steroid and high-temperature induction of the small heat-shock protein genes in Drosophila

Analysis of cytoplasmic 19 S ring-type particles in Drosophila which contain hsp 23 at normal growth temperature

Cytoplasmic 19 S particles were isolated from postpolysomal supernatants of 25 degrees C Drosophila embryos and culture cells. The particles were purified by salt extraction and sucrose gradient centrifugation. Electron microscopic investigation showed that the 19 S particles possess a ring-shaped morphology with an outer diameter of 12 nm and a hollow core of 3 nm. Biochemically the particles are characterized by a group of 16 polypeptides within the molecular weight range of 35 to 23 kDa, and small RNA molecules in the size range of 200 to 60 nucleotides. The RNP character of the particles is also shown by their buoyant density in Cs2SO4 of rho = 1.29 g/cm3 and their susceptibility to uv crosslinking and density in CsCl of rho = 1.38 g/cm3. Antibodies were raised against the proteins of the 19 S particles isolated from 25 degrees C cells and tested by immunoblotting after one- and two-dimensional gel-electrophoresis. Two of the antibodies raised cross react with the small heat-shock proteins hsp 28/27 and hsp 23. Comparative protease V8 cleavage of hsp 23 and the 23-kDa particle protein demonstrates that these two proteins are identical and that the small hsp of Drosophila must be a genuine part of the 19 S cytoplasmic ring-shaped complexes at normal growth temperature. The data support the idea of a general developmental role of some of the so-called heat-shock proteins.

Drosophila cells and ecdysterone: a model system for gene regulation

When Drosophila cell lines are exposed to physiological doses of the steroid molting hormone, ecdysterone, they enter mitotic arrest and differentiate morphologically. These responses are accompanied by specific changes in gene expression. Several enzyme activities (acetylcholinesterase, beta-galactosidase, dopa decarboxylase, and catalase) are induced and the synthesis of a cytoplasmic actin and the four small heat-shock proteins is initiated. Several of these ecdysterone inducible genes have been physically isolated and characterized, in several cases by DNA sequencing. Current studies focus on introducing cloned ecdysterone inducible genes into responsive cells by DNA mediated transfection. Once it is clear that these introduced genes acquire the normal pattern of hormone-regulated gene expression in the cell, in vitro mutagenesis can be used before transfection to modify their structure. Transient expression, then, can become a functional assay to define regions of DNA flanking the coding region of inducible genes that are needed for proper gene expression and regulation in cultured cells.