IN-VIVO ACTIVITIES OF GROEL MINICHAPERONES

Fragments encompassing the apical domain of GroEL, called minichaperon es, facilitate the refolding of several proteins in vitro without requ iring GroES, ATP, or the cage-like structure of multimeric GroEL, We h ave identified the smallest minichaperone that is active in vitro in c haperoning the refolding of rhodanese and cyclophilin A: GroEL(193-335 ). This finding raises the question of whether the minichaperones are active under more stringent conditions in vivo. The smallest minichape rones complement two temperature-sensitive Escherichia coil groEL alle les, EL44 and EL673, at 43 degrees C, Although they cannot replace Gro EL in cells in which the chromosomal groEL gene has been deleted by P1 transduction, GroEL(193-335) enhances the colony-forming ability of s uch cells when limiting amounts of GroEL are expressed from a tightly regulated plasmid. Surprisingly, we found that overexpression of GroEL prevents plaque formation by bacteriophage lambda and inhibits replic ation of the lambda origin-dependent plasmid, Lorist6, The minichapero nes also inhibit Lorist6 replication, but less markedly. The complex q uaternary structure of GroEL, its central cavity, and the structural a llosteric changes that take place on the binding of nucleotides and Gr oES are not essential for all of its functions in vivo.