Nucleic Acids Research, 1981, Vol. 9, No. 3 647-661
© 1981
CHEMISTRY |
Escherichia coli ribosome unfolding in low Mg2+ solutions observed by laser Raman spectroscopy and electron microscopy
Department of Microbiology and Immunology, Washington University School of Medicine St. Louis MO 63110 University of California, Lawrence Livermore Laboratory Livermore, CA 94550, USA
Received September 15, 1980. Ribosomes unfolded by the removal of Mg2+ at 25°C were studied by Raman spectroscopy and electron microscopy. Raman spectra showed a reduction inthe 813 cm-1 phosphodiester signal of 30S and 50S ribosomes compared to intact ribosomes, suggesting that a fraction of the ribose moieties hadshifted from the 3' endo (ordered) to the 3' exo (disordered) conformation. The maximum diameters of unfolded 30S and 50S ribosomes, judged by electron microscopy, were 1.8 and 2.5-fold greater, respectively, than those of intact ribosomes. Most unfolded 30S ribosomes had three distinct structural domains and appeared "Y-shaped"; whereas most unfolded 50S ribosomeshad four distinct domains and appeared "X-shaped". When ribosomes were partially unfolded (by brief exposure to 0.04 mM Mg2+ or EDTA), several possible intermediates in the unfolding process were observed. Both the shapes of particles and their Raman spectra reached the same final state in 0.04 mM Mg2+, where more than 50% of the rRNA phosphates aredischarged by Mg2+, as in 10 mM EOTA, where less than)% are discharged.