ISOLATION AND CHARACTERIZATION OF 6 HEAT-SHOCK TRANSCRIPTION FACTOR CDNA CLONES FROM SOYBEAN

Thermal stress in soybean seedlings causes the activation of pre-exist ing heat shock transcription factor proteins (HSFs). Activation result s in the induction of DNA binding activity which leads to the transcri ption of heat shock genes. From a soybean cDNA library we have isolate d cDNA clones corresponding to six HSF genes. Two HSF genes are expres sed constitutively at the transcriptional level, and the remaining fou r are heat-inducible. Two of the heat inducible genes are also respons ive to cadmium stress. Comparative analysis of HSF sequences indicated higher conservation of the DNA binding domain among plant HSFs than t hose from yeast or other higher eukaryotes. The putative plant HSF oli gomerization domain contains hydrophobic heptapeptide repeats characte ristic of coiled coils and seems to exist in two structural variants. The carboxy-terminal domains are reduced in size and the C-terminal he ptad repeat is degenerate.