IMMUNOSTAINING OF DNA IN ELECTRON-MICROSCOPY - AN AMPLIFICATION AND STAINING PROCEDURE FOR THIN-SECTIONS AS ALTERNATIVE TO GOLD LABELING

We describe a new electron microscopic on-section staining technique w ith high specificity and sensitivity for DNA-containing structures. Lo wicryl HM20 sections of specimens obtained by cryofixation and freeze- substitution are incubated in a first step with a primary IgM antibody specific for double-stranded DNA. The layer of bound antibodies at th e section surface is amplified in a successive step by a secondary IgG antibody. Finally, electron scattering of the antibody layer produced is enhanced by staining with a mixture of uranyl acetate and potassiu m permanganate. The applicability of the method is exemplified by the detection of shape and distribution of various types of bacterial and eukaryotic chromatin.