Morphological Analyses of Active Genes and Chromatin FREE

The visualization of chromatin with the electron microscopic approach introduced by Miller and Beatty¹ has provided important insights into gene structure and function. Information of high sensitivity may be obtained, since electron micrographs represent a visual record of the transcriptional history of a chromatin region in an individual cell. In a few cases, transcription of specific genes has been analyzed. For example, the distinctive length and tandem repeat nature of the DNA sequences that encode ribosomal RNA make the identification of active ribosomal RNA genes possible (Figure, top). A second example is the active silk fibroin genes²; this analysis was possible because differentiated cells were available in which a molecularly characterized gene was known to be highly active.

In some cases, analysis of electron micrographs has led to conclusions that go beyond existing biochemical data, thus providing important clues for future molecular and biochemical experiments. For example, electron