Characterization of Gmhsp26-A, a stress gene encoding a divergent heat shock protein of soybean: heavy-metal-induced inhibition of intron processing.

We determined the DNA sequence and mapped the corresponding transcripts of a genomic clone containing the Gmhsp26-A gene of soybean. This gene is homologous to the previously characterized cDNA clone pCE54 (E. Czarnecka, L. Edelman, F. Schöffl, and J. L. Key, Plant Mol. Biol. 3:45-58, 1984) and is expressed in response to a wide variety of physiological stresses including heat shock (HS). S1 nuclease mapping of transcripts and a comparison of the cDNA sequence with the genomic sequence indicated the presence of a soybean seedlings with either CdCl2 or CuSO4. Analysis of the 5' termini of transcripts indicated the presence of one major and at least two minor start sites. In each case, initiation occurred 27 to 30 base pairs downstream from a TATA-like motif, and thus each initiation site appears to be promoted by the activity of a separate subpromoter. The three subpromoters are all associated with sequences showing low homology to the HS consensus element of Drosophila melanogaster HS genes and are differentially induced in response to various stresses. Within the carboxyl-terminal half of the protein, hydropathy analysis of the deduced amino acid sequence indicated a high degree of relatedness to the small HS proteins. A comparison of the primary amino acid sequence of hsp26-A with sequences of the small HS proteins suggested that this stress protein is highly diverged and may therefore be specialized for stress adaptation in soybean.