Ultrastructural Probes of Chromatin within Living Human Lymphocytes

Abstract

ONE model for gene derepression in eukaryotes postulates the displacement of histones from underlying DNA templates by derepressor RNA molecules specific to the sites of transcription¹. Although the experimental data for this model were originally obtained from the analysis of isolated fractions of repressed and active chromatin², experiments analysing intact, fixed cells^{3, 4} have been less satisfactory because of the low optical resolution possible with microspectrofluorimetry, and because of the lack of chemical specificity in distinguishing DNA binding sites from RNA sites⁵. We have developed an ultrastructural molecular probe technique for use on glutar-aldehyde-fixed human bone marrow cells⁵, and now report its extension to probes of chromatin conformation states within living human lymphocytes. The probe is visualized by high-resolution electron microscopy, and distinguishes between DNA and RNA binding sites.