Structural study of translating 70 S ribosomes from Escherichia coli. I. Electron microscopy.

Translating 70 S ribosomes of Escherichia coli either in the pre-translocation or in the post-translocation state have been prepared by using the cell-free translation system in poly(U)-S-S-Sepharose columns [Methods Enzymol. (1979) 59, 382-398]. Electron microscopy study of the preparations has demonstrated that: (1) the mutual orientation of the ribosomal subunits in the translating ribosomes is the same as proposed by Lake for routine 30 S.50 S couples [J. Mol. Biol. (1976) 105, 111-130]; (2) the L7/L12 stalk of the 50 S subunit sticks out from the 70 S particle and does not join the 30 S subunit; (3) pre-translocation and post-translocation state ribosomes do not differ in mutual orientation of the subunits and in the position of the L7/L12 stalk, within the limits of electron microscopy resolution.