A Chloroplast Heat Shock Protein Has Homology to Cytoplasmic Heat Shock Proteins

Abstract

We and others have previously reported that during high temperature stress, or heat shock, specific heat shock proteins (HSPs) are transported into chloroplasts (1, 2). Soybean has two major low molecular weight chloroplast HSPs of 22 and 27 kDa, which are encoded in the nuclear genome. A cDNA clone for the 22kDa polypeptide has been isolated and used to demonstrate that the protein is initially synthesized as a 28 kDa precursor polypeptide (3). We now report on the comparison of the chloroplast HSP amino acid sequence with proteins in the PIR protein data bank and with two recently sequenced soybean cytoplasmic HSPs of low molecular weight. The data indicate that there is significant homology in the carboxy-ter-minal region between the chloroplast and cytoplasmic HSPs in soybean. Furthermore, comparisons suggest a possibly significant relationship to low molecular weight HSPs from other organisms.