AUTOMATED MICROSCOPY FOR ELECTRON TOMOGRAPHY

Instrumentation and methodology for the automatic collection of tomographic tilt series data for the three-dimensional reconstruction of single particles is described. The system consists of a Philips EM 430 TEM, with a Gatan 673 cooled slow-scan CCD camera and a Philips C400 microscope computer control unit attached. The procedure for data collection includes direct digital recording of the images on the CCD camera and the automatic measurement and correction of (a) image shifts resulting from tilting the specimen, (b) variation of defocus and (c) the eucentric height position of the specimen. Experiments are described illustrating the possibilities and limitations of automatic data collection. Data collection at a magnification of 30k shows that the exposure time of the specimen to the beam is reduced by a factor of 10-100 compared to manual operation of the TEM.