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The transposon Tn9 generates a 9 bp repeated sequence during integration.

L Johnsrud, M P Calos, J H Miller

|December 1, 1978

Summary

Transposon Tn9 integrates into the E. coli lac operon at multiple sites, forming preferred regions. Insertion is linked to a 9 base pair host DNA repeat generated during the process.

Area of Science:

Molecular Biology
Genetics
Microbiology

Background:

The lac operon in Escherichia coli is a well-studied genetic system for understanding gene regulation.
Transposable elements, like transposon Tn9, are mobile DNA sequences that can alter gene function and genome structure.

Purpose of the Study:

To genetically and physically map insertions of the transposon Tn9 within the lac operon of E. coli.
To characterize the sequence features associated with Tn9 integration into the host genome.

Main Methods:

Genetic mapping of 70 Tn9 insertions into the lacI and lacZ genes.
Restriction mapping to analyze insertion sites.
DNA sequencing of three independent Tn9 insertions.

Main Results:

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Tn9 demonstrated insertion into at least 50 distinct sites within the lacI and lacZ genes, originating from a common chromosomal point.
Analysis revealed preferred insertion regions, characterized by multiple integration points within localized areas.
Sequence analysis showed Tn9 integration is associated with a 9 base pair direct repeat of host DNA, generated during insertion.

Conclusions:

Transposon Tn9 exhibits site-specificity in its integration into the E. coli lac operon, with preferred but multiple target sites.
The integration mechanism of Tn9 involves the generation of a short direct repeat of host DNA sequence at the insertion junction.