You are carrying out experiments examining the DNase I digestion results in nuclei isolated from several different mammalian cells. Your results show that there is preferential digestion of a set of unique DNA sequences in each cell type. Which of the following characteristics of chromatin in these sequences best explains your observations?

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Quizplus · Accepted Answer

Transcriptionally active chromatin is more open and accessible, making it more susceptible to DNase I digestion. This explains the preferential digestion of unique DNA sequences in different cell types, as these sequences are likely to be actively transcribed in those specific cells.  DNase I is a versatile enzyme that nonspecifically cleaves DNA. DNA within chromosomes is complexed with a variety of different proteins including the histones. The protein-DNA complexes can restrict the access of DNase I to the DNA strand. Various types of chromatin structure exist across a wide range of DNA and the structure changes in a dynamic way. Transcriptionally active regions of the chromosomes are in a much more open configuration than transcriptionally silent regions. Therefore, the DNA in regions of the chromosomes from various cell types that are transcriptionally active will more likely be accessible to digestion by DNase I.

You Are Carrying Out Experiments Examining the DNase I Digestion