Host specificity of DNA produced by Escherichia coli. XVI. Phage lambda DNA carries a single site of affinity for A-specific restriction and modification |
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Authors: | Werner Arber Alain Rifat Danièle Wauters-Willems and Urs Kühnlein |
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Institution: | (1) Department of Molecular Biology, University of California, 94720 Berkeley, Calif, USA;(2) Department of Molecular Biology, University of Geneva, CH-1211 Geneva, Switzerland;(3) Present address: Department of Biochemistry, Stanford University Medical School, 94305 Stanford, Calif, USA;(4) Biozentrum der Universität, CH-4056 Basel, Schweiz |
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Abstract: | Summary Bacteria with A-specific restriction plate unmodified phage with an efficiency of 10-2. One mutational event can produce restriction insensitive (sAo) mutants of . These differ from the original sA form of by no other property than their response to A-host specificity. Two-parental phage crosses involving sA and sAo, respectively, as non-selective marker allowed to map sA between genes cII and O. These data indicate that sA is the only site on DNA with affinity for A-specific restriction. DNA is thus an interesting substrate in in vitro A-specific restriction and modification. Using an assay based on the infectivity of DNA on helper-infected bacteria, A-specific modification activity was found in partially purified sonicates of bacteria with A-host specificity. In parallel to modification, 3H-methyl label from s-adenosylmethionine, the only cofactor required for modification, was transferred to unmodified DNA. No association of radioactivity was observed in control experiments with DNA from either modified ·A or from a sAo mutant. These data suggest that A-specific modification is brought about by DNA methylation and that the sAo mutation not only abolished the affinity for A-specific restriction, but also for A-specific modification. |
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