You are testing the activity of an enzyme you have isolated from bovine pancreas. You find that when this enzyme is added to nuclei isolated from adipocytes and the products are subsequently analyzed by gel electrophoresis that the DNA in the nuclei is degraded into relatively discrete sizes approximately 150 bp in length. Which of the following most likely represents the enzyme activity in your pancreatic preparation?

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Quizplus · Accepted Answer

DNase I is an enzyme that non-specifically cleaves DNA, and it is known to degrade DNA into fragments of approximately 150-200 base pairs, which corresponds to the length of DNA wrapped around a nucleosome.  DNase I randomly hydrolyzes the phosphodiester bonds of double-stranded DNA. The enzyme is used in the identification of regions of DNA that are bound by protein, and thereby protected from DNase I digestion. Since the nucleosomes would protect regions of DNA of approximately 150 bp in length, DNase I digestion would result in the generation of a high-proportion DNA fragments of that length. Although restriction enzymes digest DNA at discrete sequence motifs, the distribution of these motifs is essentially randomly distributed, and therefore would not result in most of the DNA being found as 150-bp fragments.

You Are Testing the Activity of an Enzyme You Have