3-DIMENSIONAL RECONSTRUCTION OF THE MAMMALIAN CENTRIOLE FROM CRYOELECTRON MICROGRAPHS - THE USE OF COMMON LINES FOR ORIENTATION AND ALIGNMENT

The microtubule organizing center of the animal cell (S. D. Fuller et al., 1992, Curr. Opin. Struct. Biol. 2, 264-274; D. M. Glover et al., 1993, Sci. Am. 268, 62-68; E. B. Wilson, 1925), (The Cell in Developme nt and Heredity) comprises two centrioles and the pericentriolar mater ial. We have completed several three-dimensional reconstructions of in dividual centrioles from tilt series of cryoelectron micrographs, The reconstruction procedure uses minimization of the common lines residua l to define the orientation of the centriolar ninefold symmetry axis a nd then uses this symmetry to generate a structure by weighted backpro jection to 28-nm resolution, Many of the features of these reconstruct ions agree with previous, conventional transmission electron microscop y studies (M. Paintrand et al., 1992, J. Struct. Biol. 108, 107-128). The microtubule barrel of the centriole is roughly 500 nm long and 300 nm in diameter and the microtubule bundles appear to taper toward the distal end, In addition, we see a handedness to the pericentriolar ma terial at the base (distal end) of the centriole which is opposite to the skew of the microtubule triplets, The region at which the microtub ule barrel joins this base is intriguingly complex and includes an int ernal cylindrical feature which is a site of gamma tubulin localizatio n. (C) 1997 Academic Press.