[Regulation of genetic expression during the transfer of information from the nucleus to the cytoplasm].

Abstract

In eukaryotes, the transfer of genetic information from the genome to its final site of phenotypic expression is a multistep process. These steps are described and the mechanisms of regulation operating at these various levels are reviewed. The heat shock response in two diptera, Drosophila and Chironomus, is described as a model system to illustrate the existence of regulation mechanisms at different levels of genetic information transfer. In Chironomus tentans like in Drosophila, a short heat shock (10 min, 39 degrees C) treatment induces the synthesis of at least 8 new proteins. This is accompanied by a drastic reduction in the synthesis of the normal proteins that in those synthesized prior to the shock. The localisation of these induced proteins has been studied by microdissection of the various intranuclear and intracellular compartments of salivary glands. While most of these have a ubiquitous distribution, one induced protein (34 000 Daltons) is exclusively localized in the nucleus. Another one (25 000 Daltons) is mainly concentrated in a particulate form which cosediments with ribosomes. Arsenite and anaerobiosis do not induce a heat shock mimicking response in Chironomus. The induction mechanisms as well as the transcriptional and translational controls operating during the heat shock response are discussed.