Upstream sequences required for efficient expression of a soybean heat shock gene.

A soybean gene (Gmhsp17.5-E) encoding a small heat shock protein was introduced into primary sunflower tumors via T-DNA-mediated transformation. RNA blot hybridizations and S1-nuclease hybrid protection studies indicated that the heat shock gene containing 3.25 kilobases of 5'-flanking sequences was strongly transcribed in a thermoinducible (40 degrees C) manner. Transcriptional induction also occurred to a lesser extent upon treatment of whole tumors with sodium arsenite and CdCl2. Basal (26 degrees C) transcription was not detected in soybean seedlings, but it was quite evident in transformed tumor tissue. A 5' deletion to -1,175 base pairs with respect to the CAP site had no effect on the levels of thermoinducible transcription, but it resulted in a large increase in basal transcription. Further removal of DNA sequences (including the TATA-distal heat shock consensus element) to -95 base pairs reduced thermoinducible transcription by 95% and also greatly decreased basal transcription. The termini of the Gmhsp17.5-E RNA in the tumor were generally the same as those present in soybean RNA, with the exception of several additional 3' termini.