From the Chromosomal Loops and the Scaffold to the Classic Bands of Metaphase Chromosomes
This extract was created in the absence of an abstract.
Excerpt
INTRODUCTION
Chromatin Loops
A structural study of the metaphase chromosome is a daunting activity with inadequate tools: The electron or optical microscopes are either too detailed or too coarse to elucidate the packaging mode of the chromatin fiber, and the biochemical approach falls easy prey to the criticism of destructive interference. To make matters worse, native chromosomes display few structural features, appearing as cylindrical structures quite homogeneously stuffed with a nucleoprotein fiber. It is necessary to try to elicit the structure from chromosomes; cytogeneticists have been doing this, albeit for a different purpose, using remarkably harsh methodologies.
Despite this gloom, we consider the notion of chromatin loops (∼ 100 kb) as solid. The looped organization of DNA was originally observed by electron microscopy in histone-depleted metaphase chromosomes also using relatively harsh methodologies (histone and other proteins were displaced by competition with the polyanions dextran sulfate and heparin) to unfold chromosomes...
