Haloarcula marismortui 50S subunit - Complementarity of electron microscopy and X-ray crystallographic information

The large 50S subunit of the Haloarcula marismortui 70S ribosome was solved to 19 Angstrom using cryoelectron microscopy and single particle reconstru ction techniques and to 9 Angstrom using X-ray crystallography In the latte r case, phases were determined by multiple isomorphous replacement and anom alous scattering from three heavy atom derivatives. The availability of X-r ay and electron microscopy (ERI) data has made it possible to compare the r esults of the two experimental methods, In the flexible regions of the 50S subunit, small differences in the mass distribution were detected. These di fferences can be attributed to the influence of packing in the crystal cell . The rotationally averaged power spectra of X-ray and EM were compared in an overlapping spatial frequency range from 60 to 13 Angstrom. The resultin g ratio of X-ray to EM power ranges from 1 to 15, reflecting a progressivel y larger underestimation of the Fourier amplitudes by the electronmicroscop e. (C) 1999 Academic Press.