Heat‐Shock Peptides in Drosophila hydei and Their Synthesis in vitro

The protein‐synthetic response to a heat shock, namely the synthesis of a number of new peptides, of Drosophila hydei salivary glands and tissue‐culture cells appears qualitatively the same when analyzed by dodecylsulphate electrophoresis, except that in tissue‐culture cells an additional band at 25500 M r appears while the 20000‐ M r peptide, found in salivary glands, is sometimes absent depending on the cell line used. Further analysis of the heat‐shock peptides by two‐dimensional electrophoresis showed that the response of salivary glands and embryonic cells also differs: two major proteins with a molecular weight around 26000 were found in embryos, one of which may be identical to the 25500‐ M r protein seen in cultured cells. Two‐dimensional heat‐shock patterns are further characterized by a number of minor polypeptides whose position and intensity vary slightly from one tissue to another. Polysomal poly(A)‐containing RNA extracted from heat‐shocked embryos and tissue‐culture cells directed the synthesis in a wheat germ extract of all heat‐shock peptides found in vivo in the same tissue. Therefore, the appearance of one additional protein in embryos and tissue‐culture cells does not arise from tissue‐specific post‐translational modifications but must be due to the induction of an additional gene as compared to salivary glands. A similar conclusion may hold for the minor heat‐shock proteins found in the two‐dimensional patterns in vivo as well as in vitro.