Chapter 10, Problem 27P

Genomic DNA from the nematode worm Caenorhabditiselegansis organized by nucleosomes in the manner typical of eukaryotic genomes, with $145$ bp encircling each nucleosome and approximately 55 bp in linker DNA. When C. elegans chromatin is carefully isolated, stripped of nonhistone proteins, and placed in an appropriate buffer, the chromatin decondenses to the $\text{10-nm}$ fiber structure. Suppose researchers mix a sample of $\text{10-nm–fiber}$ chromatin with a large amount of the enzyme DNase I that randomly cleaves DNA in regions not protected by bound protein. Next, they remove the nucleosomes, separate the DNA fragments by gel electrophoresis, and stain all the DNA fragments in the gel.

Approximately what range of DNA fragment sizes do you expect to see in the stained electrophoresis gel? How many bands will be visible on the gel?

Explain the origin of DNA fragments seen in the gel.

How do the expected results support the $\text{10-nm–fiber}$ model of chromatin?