High resolution electron microscope studies of chromosomal fibers

Abstract

Techniques are described for mounting and visualizing biological macromolecules for high resolution electron microscopy. Standard techniques are included in a discussion of new methods designed to provide the highest structural resolution. Methods are also discussed for handling samples on the grid, for making accurate size measurements at the 20 A level, and for photographically enhancing image contrast. The application of these techniques to the study of the binding of DNA polymerase to DNA is described. It is shown that the electron micrographs of this material are in agreement with the model proposed by Dr. Arthur Kornberg. A model is described which locates several active sites on the enzyme. The chromosomal material of the protozoan tetrahymena has been isolated and characterized by biochemical techniques and by electron microscopy. This material is shown to be typical of chromatin of higher creatures. Comparison with other chromatins discloses that the genome of tetrahymena is highly template active and has a relatively simple genetic construction. High resolution electron microscope procedures developed in this work have been combined with standard biochemical techniques to give a comprehensive picture of the structure of interphase chromosome fibers. The distribution of the chromosomal proteins along its DNA is discussed.