Cryo-electron microscopy reconstructions...

A: Cryo-electron microscopy (cryo-EM) of 40S ribosomal subunit at ~20-Å resolution.

B: Cryo-EM reconstruction of a complex between the 40S ribosomal subunit (yellow) and the internal ribosome entry site (IRES) RNA of hepatitis C virus (purple). Comparison with the structure in Figure A reveals a conformational change in the 40S subunit (upper right) induced by IRES binding.

C: Representative RNA helices fit the dimensions of the IRES RNA density.

From Spahn, C.M.T., Kieft, J.S., Grassucci, R.A., Penczek, P., Zhou, K., Doudna, J.A., and Frank, J. 2001. Science 291:1959–1962. © 2001 American Association for the Advancement of Science.