The 70 kDa family of Heat shock proteins(Hsp70s)is involved in a number of seemingly disparate cellular functions,including folding of nascent proteins,break up of misfolded protein aggregates,and translocation of proteins across membranes.They act through the binding and release of substrate proteins,accompanied by hydrolysis of ATP.Chloroplast stromal Hsp70 plays a crucial role in the import of proteins into plastids.