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Structure of inserted bacteriophage Mu-1 DNA and physical mapping of bacterial genes by Mu-1 DNA insertion
Abstract:
It is shown, by electron microscope observation of the structures of heteroduplexes, that Mu-1 DNA inserted into the bacterial episomes Flac and F(8)[1] is collinear with, rather than a circulation permutation of, the DNA of the mature Mu-1 bacteriophage. Observation of the position of the inserted Mu defines a point within the gene that has been inactivated (the lacI gene for Flac and a transfer gene in F(8)[1] in these particular instances). These examples illustrate a new, general method for physical gene mapping. The episome with Mu DNA inserted into F(8)[1] [i.e., F(8)[1](Mu)], although derived from a single colony, is heterogeneous in that a self-renatured sample shows a nonhomology loop of length 3.0 kb. This nonhomology loop, which has previously been observed in mature Mu-1 DNA, is due to an inversion.
Insights
Electron microscopy reveals Mu-1 DNA insertion into bacterial episomes is collinear, not permuted. This enables a new physical gene mapping method by identifying inactivated genes and DNA inversions.
Area of Science:
- Molecular Biology
- Genetics
- Microbiology
Background:
- Bacterial episomes like Flac and F(8)[1] can host foreign DNA.
- Bacteriophage Mu-1 DNA structure and insertion mechanisms are of interest.
- Physical gene mapping provides precise localization of genetic elements.
Purpose of the Study:
- To investigate the structural arrangement of Mu-1 DNA within bacterial episomes.
- To demonstrate a novel method for physical gene mapping using Mu-1 DNA insertions.
- To characterize the heterogeneity observed in F(8)[1](Mu) episomes.
Main Methods:
- Electron microscopy of heteroduplex DNA structures.
- Analysis of Mu-1 DNA insertion sites within Flac and F(8)[1] episomes.
- Characterization of DNA nonhomology loops in self-renatured episomal DNA.
Main Results:
- Mu-1 DNA insertion into Flac and F(8)[1] episomes is collinear with mature Mu-1 DNA.
- The insertion position precisely maps inactivated genes (lacI and transfer genes).
- F(8)[1](Mu) episomes exhibit heterogeneity, including a 3.0 kb nonhomology loop due to inversion.
Conclusions:
- Mu-1 DNA insertion provides a reliable method for physical gene mapping.
- The observed nonhomology loop in F(8)[1](Mu) is consistent with known Mu-1 DNA inversions.
- This study establishes a new approach for detailed genetic analysis in bacteria.