Instrumentation for the three-dimensional reconstruction of cellular organelles by electron microscopy.

ABSTRACT

Instrumental additions to the Zeiss EM-10 electron microscope are described as well as a flat-bed scanning densitometer specifically intended for the tomographic assessment of the three-dimensional structure of chromosomes. The additions to the electron microscope consist of two ion-getter pumps, reducing contamination to 0.0004 A/s. Further, a device was attached that made it possible to indicate through markers in the final negative the direction of the axis of tilt of the goniometer stage, i.e. markers indicating the tomographic axis in the digitized image. The flat-bed scanner permits correction of image rotation caused by refocusing. The preparation itself contains polystyrene latex spheres, i.e. objects the shape of which is independent of rotation (tilt). These can be used for computational corrections of the digitized image.