TARGETING OF GROEL TO SECA ON THE CYTOPLASMIC MEMBRANE OF ESCHERICHIA-COLI

Chaperonin GroEL has been found to interact with isolated cytoplasmic membrane of Escherichia coli. Interaction requires Mg ions, whereas Mg ATP inhibits, and inhibition is stronger in the presence of co-chapero nin GroES. ''Heat-shock'' of the membrane at 45 degrees C destroys irr eversibly its ability to bind GroEL, The binding of GroEL is character ized by saturation with a maximum of about 100 pmol GroEL bound per mg of total membrane protein, indicating a limited capacity and specific ity of the membrane to bind GroEL. According to results of immunoblott ing analysis and cleavable photoactivable cross-linking, a membrane ta rget of GroEL is SecA, a protein known as a central component of the t ranslocation machinery, Moreover, in some cases GroEL could modulate a cycle of association of SecA with the membrane by stimulating release of SecA from the membrane. A physiological role of targeting of GroEL in or close to the protein-conducting membrane apparatus is discussed .