Treatment of gently prepared lysates of Escherichia coli with single-strand-specific endonuclease (SI or from mung beans) results in the release of about 90% of the DNA from membranes, as determined by the M band technique. The released DNA has an average molecular weight of about 1.2 X 108. Data obtained with endonuclease SI fit a mathematical model in which substrate sites are at or near membrane attachment sites. Data obtained with pancreatic deoxyribonuclease or x-rays fit a model for double-strand breaks at random sites along the DNA. Fitting data to these models, we estimate that there are 18 ± 5 membrane attachment sites. The DNA remaining after SI nuclease treatment is enriched for the region near the origin of chromosome replication. Therefore, attachment at this region appears to be chemically different from that at the other sites along the DNA.


Molecular, Cellular and Biomedical Sciences

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Proceedings of the National Academy of Sciences


National Academy of Sciences

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