VISUALIZATION OF A LARGE CONFORMATION CHANGE OF RIBOSOMES IN ESCHERICHIA-COLI-CELLS STARVED FOR TRYPTOPHAN OR TREATED WITH KIRROMYCIN

Computer-aided electron tomography has been used to visualize ribosome s in Escherichia coli cells treated with kirromycin. This antibiotic s tops bacterial growth by blocking the release of EF-Tu.GDP from the ri bosome after GTP cleavage. Ribosomes in the kirromycin-treated cells a re very compact, with the two subunits in close contact with each othe r. This closed structure is different from the open structure with spa tially separated subunits that characterizes ribosomes in tryptophan-s tarved cells, giving deficiency for tryptophanyl.tRNA. A comparison of ribosomes in exponentially growing bacteria suggests that most riboso mes in an undefined working mode are in the closed conformation. (C) 1 998 Academic Press.