Transcription of a Drosophila heat shock gene is heat-induced in Xenopus oocytes.

Xenopus cells, like many other eukaryotic cells, respond to heat treatments by increasing the rate of synthesis of a few characteristic proteins, the heat shock proteins. Because of the generality of this response, it seemed possible to examine the expression of isolated heat shock genes in a heterologous system. Phage 122 DNA, containing two identical genes coding for the Drosophila 70,000-dalton heat shock protein (hsp70 genes), was microinjected into Xenopus oocyte nuclei. The Drosophila hsp70 genes are transcribed efficiently in heat-treated oocytes (35-37 degrees C) to give RNA of the correct size and sequence content. Transcription is sensitive to low levels of alpha-amanitin and therefore is carried out by RNA polymerase II. At normal temperatures (20-28 degrees C) essentially no Drosophila-specific RNA is formed. The isolated insert fragment of phage 122 also gives RNA of correct length in heat-treated oocytes which hybridizes to the coding segment of Drosophila hsp70 genes only. At normal temperatures, however, its rate of transcription is variable and only RNA heterogeneous in size is formed.