A NOVEL ATPASE COMPLEX SELECTIVELY ACCUMULATED UPON HEAT-SHOCK IS A MAJOR CELLULAR-COMPONENT OF THERMOPHILIC ARCHAEBACTERIA

We have discovered a large cylindrical protein complex which is an abundant component of the cytoplasm of extremely thermophilic archaebacteria. Structural analysis by image processing of electron micrographs suggests that the complex is composed of two stacked rings of eight subunits each; the rings enclose a central channel. The complex purified from the hyperthermophile Pyrodictium occultum is composed of equal quantities of two polypeptides Of M(r) 56 000 and 59 000. It exhibits an extremely thermostable ATPase activity with a temperature optimum of 100-degrees-C. The basal level of the ATPase complex in the cell is high, and it becomes highly enriched as a result of heat shock (shift from 102-degrees-C to 108-degrees-C) or balanced growth at temperatures near the physiological upper limit. Immunoblotting results indicate that a related protein is present in most thermophilic archaebacteria and in Escherichia coli. This protein complex may play an important role in the adaptation of thermophilic archaebacteria to life at high temperature.