Differential expression of heat‐shock proteins and spontaneous synthesis of HSP70 during the life cycle of Blastocladiella emersonii

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Abstract
The heat‐shock response in Blastocladiella emersonii is dependent on the developmental stage. Cells exposed to elevated temperatures at different stages of the life cycle (sporulation, germination or growth) show a differential synthesis of heat‐shock proteins (hsps). Of a total of 22 polypeptides induced, particular subsets of hsps appear in each phase, demonstrating a non‐coordinate heat‐shock gene expression. In contrast, heat‐shock‐related proteins (hsp76, hsp70, hsp39a) are spontaneously expressed at a high level during sporulation. By the criteria of two‐dimensional gel electrophoresis and partial proteolysis mapping, the 70 000‐Da protein, whose synthesis is induced spontaneously during sporulation, is indistinguishable from the heat‐inducible hsp70. The techniques of in vitro translation, and Northern analysis using a Drosophila hsp70 probe, demonstrated that enhanced synthesis of hsp70, which occurs during heat‐shock treatment and spontaneously during sporulation, is associated with an accumulation of hsp70 mRNA. These observations suggest that hsp70 gene expression is induced during sporulation.