Intracellular localization of a group II chaperonin indicates a membrane-related function.

Chaperonins are protein complexes that are believed to function as part of a protein folding system in the cytoplasm of the cell. We observed, however, that the group II chaperonins known as rosettasomes in the hyperthermophilic archaeon Sulfolobus shibatae, are not cytoplasmic but membrane associated. This association was observed in cultures grown at 60 degrees C and 76 degrees C or heat-shocked at 85 degrees C by using immunofluorescence microscopy and in thick sections of rapidly frozen cells grown at 76 degrees C by using immunogold electron microscopy.