The organization of the microtubule network of eukariotic cells is controlled by the centrosome. This organelle which duplicates once during the cell cycle comprises two centrioles and a dense filamentous material called pericentriolar material. The centrioles are cylinders of ≈ 0.25 μm in diameter and ≈ 0.5μm in length and are composed of 9 microtubule triplets at the proximal end and 9 doublets at the distal end. For the last 50 years the centrosome and the centrioles in particular have been the object of many optical and electron microscopy studies. But, in spite of their highly symmetric organization, their fine structure is still not well understood. The reconstruction presented here is a substantial step forward towards a more detailed understanding of their structure.

Centrosomes were isolated from a human lymphoblastoma cell line (1). 10 nm gold particles were applied to formvar-carbon coated grids to provide markers for the alignment procedure (2,3). Centrosomes were centrifuged onto the grids and negatively stained.