Expression of microinjected hsp 70/CAT and hsp 30/CAT chimeric genes in developing Xenopus laevis embryos

The expression of microinjected chimeric genes containing Drosophila hsp 70 and Xenopus hsp 70 and hsp 30 promoters linked to the reporter gene coding for bacterial chloramphenicol acetyltransferase (CAT) was examined during early development of Xenopus laevis. Heat-inducible expression of fusion genes containing either the Drosophila hsp 70 promoter (1100 bp) or the Xenopus hsp 70 promoter (750 bp) was first detectable after the midblastula stage of development. This coincides with the embryonic stage at which the endogenous hsp 70 gene is first heat-inducible. A Xenopus hsp 30/CAT fusion gene containing 350 bp of promoter sequences was also heat-inducible after the midblastula stage unlike the endogenous hsp 30 genes which were not heat-inducible until the early tailbud stage (stage 23-24). Sequences that are present within either the coding or 3' region of the hsp 30 clone do not cause the microinjected hsp 30 gene to be developmentally regulated in a normal manner. Additionally, microinjected hsp 30 gene sequences have no effect on the developmental regulation of endogenous hsp 30 genes which continue to be activated at the tailbud stage of development. Our data suggest, that an inhibitory system, which may control the expression of the endogenous hsp 30 gene during development, does not regulate the expression of the injected hsp 30 gene.     

Protein/DNA architecture of the DNase I hypersensitive region of the Drosophila hsp26 promoter.

Genomic footprinting on the Drosophila hsp26 promoter in isolated nuclei has shown that a TATA box binding factor is present before and after induction by heat shock, while three of the seven heat shock consensus sequences 5' of the gene are occupied (presumably by heat shock factor, HSF) specifically on heat shock. The sites of HSF interaction are separated by greater than 200 bp of which approximately 150 bp are bound to the surface of a nucleosome. The juxtaposition of these various macromolecules on the DNA suggests a basis for the major DNase I hypersensitive site 5' of hsp26 and a novel tertiary structure for the promoter complex.