A STRATEGY FOR ELECTRON TOMOGRAPHIC DATA-COLLECTION AND CRYSTALLOGRAPHIC RECONSTRUCTION OF BIOLOGICAL BUNDLES

Structures of highly ordered biological bundles have unique features w hich call for special experimental and computational methods in electr on cryomicroscopy. They can be considered as three dimensional quasi-c rystals and reconstructed using a crystallographic approach. However, they are neither ''infinitely'' large with respect to the borders of t he bundle, nor are they a single unit cell in thickness along the view ing direction, Also, because of their shape, bundles do not generally have a preferred azimuthal orientation, which poses challenges for ori entation estimation and refinement. We developed a strategy for record ing and processing electron cryomicroscopic images that differs fi om classical two-dimensional crystalline reconstruction techniques. These developments allowed us to merge data hom tomographic tilt series of ice-embedded acrosomal bundles. The goal is to determine accurately am plitudes and phases at the diffraction maxima in terms of hkl indices, and compute a three-dimensional map from the diffraction data. (C) 19 97 Academic Press.