The pattern of protein synthesis changes rapidly and dramatically when the growth temperature of soybean seedling tissue is increased from 280C (normal) to about 400C (heat shock). The synthesis of normal proteins is greatly decreased and a new set of proteins, "heat shock proteins," is induced. The'heat shock proteins of soybean consist of 10 new bands on one-dimensional NaDodSO4 gels; a more complex pattern is observed on two-dimensional gels. When the tissue is returned to. 28!C after 4 hr at 40°C, there is progressive decline in the synthesis of heat shock proteins and reappearance of a normal pattern of-synthesis by 3 or 4 hr. In vitro translation of poly(A)+RNAs isolated from tissues grown at 28 and 400C shows that the heat shock proteins are translated from a new set of mRNAs induced at 400C; furthermore, the abundant class mRNAs for many of the normal proteins persist even though they -are translated weakly (or not;at all) in vivo at40 or 42.5 YC. The heat shock response in soybean appears similar to'the much studied heat shock phenomenon in Drosophila.Protein synthesis responds rapidly and dramatically to stress in a wide range of organisms. In soybean seedlings exposed to anaerobic conditions or incubation in dinitrophenol there is a fast read-out of polyribosomes which results--in a rapid transition from polyribosomes to mostly monoribosomes and a new low rate of protein synthesis (1). Water stress in maize seedlings similarly leads to a rapid loss of polyribosomes and low levels' of protein synthesis (e.g., refs. 2 and 3). In the case of anaerobiosis, much of the pre-stress mRNA persists for several hours during the anaerobic treatment in both soybean (1) and maize (4). In the case of maize roots, at least, the anaerobic treatment also results in the synthesis of a small number of new mRNAs and proteins and, as noted above, a greatly decreased' (or no) level of translation of the pre-stress mRNAs (4,5).These results together with those relating.to the much-stud. ied heat shock phenomenon of.Drosophila (see ref. 6) suggest that these changes in the patterns of mRNA and protein synthesis result from the induction by the stress agentof some regulatory event(s). In Drosophila (6) and a number of other systems studied to date (e.g., refs. 7-10) a change from the normal growth temperature to an increased temperature (e.g.,. 250C to 370C in the case of Drosophila) results in the shut-off (or reduction) of normal protein synthesis in concert with the induction of a set of "heat shock proteins." The heat shock response seems to be representative of a more general stress response because a wide range of stress agents induce the heat shock proteins in Drosophila (6) and a set of similar proteins in other systems (e.g., refs. 7 and 9).Except for the alcohol dehydrogenases induced by anaerobiosis in maize (4), the identity of the stress proteins remains obscure. There is some progress, however, in localizing at the subeellular level some of the heat shock proteins in Drosophila (e.g., refs. 11 and 12).We...

The 70-100% ammonium sulfate fraction of postribosomal supernatant of heat shocked soybean seedlings contained a high percentage of all of the heat shock proteins. The proteins in this fraction were resistant to heat denaturation, as judged by their unpelletability after heat treatment. Moreover, this fraction, when added to the postribosomal supernatant from control (nonheat shocked) seedlings, showed a significant ability to protect the control proteins from heat denaturation. Heated at 55°C, some 50% of the control proteins, which were normally denatured after heat treatment, were protected for at least 1 h when heat shock proteins-enriched fraction was added. The degree of protection was proportional to the amount of heat shock proteins-enriched fraction added. However, when the ammonium sulfate fraction prepared from the seedlings with a heat treatment at 40° C for 3 h followed with a brief heat shock at 45 °C which depleted most of the 15-18 kDa and partial 68-70 kDa, 24 kDa and 22 kDa heat shock proteins was added the effectiveness in preventing heat denaturation was lost. This suggests that the heat shock proteins of 15-18 kDa with those of 68-70 kDa and perhaps 24 kDa and 22 kDa are important for providing the protection from heat denaturation.

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Two rice cDNA clones pTS1 and pTS3 were screened at reduced stringency from a cDNA library generated from rice seedling poly(A) RNA by a partial cDNA fragment of soybean 17.5E (pCE53). The rice seedlings were induced at 41 ° C for 2 h before harvest for RNA extraction. Both clones were identified by a hybrid-selected in vitro translation assay and proved to belong to the low-molecular-mass heat-shock protein group (16-20 kDa). The rice pTS1 clone has an open reading frame encoding a 150 amino acid residue 16.9kDa protein which is 72.3~o, 75.3~o and 83.7~o identical to soybean HSP 17.5E [1], pea HSP 179a [2] and wheat C5-8 [3], respectively. On the other hand, the pTS3 cDNA clone encodes a 155 amino acid residue 17.3 kDa protein which is 70.9~o, 73.1~o, 67.5~o identical to soybean HSP 17.5E, pea HSP 179a and wheat C5-8, respectively. A series of pairwise sequence comparisons show that the two eDNA clones belong to the class I low-molecular-weight heatshock protein family. Among the members of this family, they share a higher homology at the carboxyl terminal than at the amino terminal, as all HSPs do. Both the cDNA and deduced amino acid sequences of the two clones are shown in Fig. 1 and Fig. 2.

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