A recombinant rice 16.9-kda heat shock protein can provide thermoprotection in vitro

It is difficult to obtain large amounts of purified low-molecular-mass heat shock proteins (LMM HSPs), which are unique to plants, for biochemical and physiological studies. Therefore, an attempt was made to produce such a HSP by applying recombinant DNA technology. We fused the cDNA for a rice class I 16.9-kDa HSP, pTSl, to the gene for glutathione S-transferase (GST) of Schistosoma japonicum and we obtained large amounts of the fusion protein from transformed Escherichia coli cells. In addition, we found that the 16.9-kDa HSP obtained by cleavage of the recombinant protein could also form a protein complex of ̃310 kDa under non-denaturing conditions as can the small, native, class I HSPs from heat-shocked rice seedlings. An assay in vitro to examine the thermoprotection of rice soluble proteins from heat denaturation revealed the strong stabilizing effect of the recombinant HSP.