Mild heat treatments applied to whole animals or cell cultures of Drosophila prior to lethal heat shocks result in increased survival and protection against phenocopy induction. The optimal condition for the preliminary mild heat treatment is that which induces the synthesis of heat-shock proteins but does not turn off the protein synthesis that is in progress. Recovery of protein synthesis but not RNA synthesis following a drastic heat shock is much enhanced by the pretreatments. The results suggest that the protection for survival and against phenocopy induction is due to storage of messenger RNA.Key words: drosophila, gene regulation, heat shock, protection phenocopies, survival I NTROD UCTl ON We recently described [ I ] a series of phenocopies that are induced in Drosophila melanogaster by subjecting pupa to heat shock at specific stages of development. Three of the phenocopies produced by shocks at successive intervals closely resemble the mutants hook and javelin which are involved in determining the structure of the scutellar bristles of the adult fly. We have also shown that the conditions used for phenocopy induction, turn off, for a time, both transciptional and translational activities in Drosophila tissues [ 1 , 2 ] . Subsequently, translation resumes long before reactivation of transcription [ l ] . These findings show that heat shock can result in storage of mRNAs in keeping with the observations of McKenzie et a1 [ 131 and Mirault et a1 [14] . Furthermore these observations provide a reasonable basis for interpretation of the heat-shock protection phenomenon described by Milkman several years ago [3,4] . Milkman and collaborators demonstrated that when Drosophila pupa (24 hours) were subjected to a mild heat shock prior to one that would be lethal alone, some animals would survive. They also reported that a pretreatment of this kind would prevent the induction of a phenocopy of the mutant crossveinless.

Pupae of Drosophila melanogaster were heat-shocked under conditions required to induce phenocopies in more than 90% of the flies that subsequently emerge. The effects of these treatments on protein synthesis in two tissues (thoracic epithelium and brain) were followed for several hours after the heat treatments. Results from pulse-labeling and protein separations on sodium dodecylsulfate (SDS) acrylamide gels showed a virtually complete cessation of protein synthesis immediately after the shock, followed by a noncoordinate resumption of the starting pattern. Similar experiments following double heat shocks demonstrated a more rapid resumption of synthesis of heat shock proteins after two successive heat treatments than after a single one.

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We describe variants of three heat-shock proteins of Drosophilg melanogaster and their use to map the chromosome regions that contain the coding sequences for these proteins. All three map to a region on chromosome 3L that includes only one heat-shock puff, designated as 67B. The results imply that the genes coding for at least three heat-shock proteins are included within the 67B region.