SV40 Chromatin Structure
Some features of the 80S nucleoprotein extracted from the nuclei of SV40-infected cells have been explored. A region of the SV40 genome including the origin of replication and about 400 base pairs of adjacent sequence is contained in an altered chromatin structure, rendering it hypersensitive to endonuclease digestion and accessible to exonuclease digestion once an endonucleolytic cut has been introduced. DNA sequences within this region are responsible for the nuclease-sensitive configuration. At least two genetic elements, each of which can generate a hypersensitive site, have been mapped to the region between nucleotide positions 37 and 287. Insertion of segments of DNA at position 37/38 does not disrupt the hypersensitive site but moves it away from the origin of replication. Insertion of 90 base pairs or more causes the origin to lie outside the hypersensitive site and the resulting genome replicates inefficiently. This result suggests that efficient functioning of the viral replication origin may depend on location within a hypersensitive site in the chromatin. The same may be true for viral promoters although the genetic evidence is incomplete.
KeywordsChromatin Structure Hypersensitive Site Staphylococcal Nuclease Exonuclease Digestion Endogenous Nuclease
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