Transposition of the Escherichia coli insertion element gamma generates a five-base-pair repeat

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• The Escherichia coli insertion element gamma delta is a mobile genetic element.
• Understanding the mechanisms of transposition is crucial for comprehending genome evolution and plasticity.

Purpose of the Study:

• To determine the DNA sequences flanking the termini of the gamma delta element.
• To investigate the role of target DNA duplications in gamma delta transposition.
• To compare the terminal sequences of gamma delta with other mobile genetic elements.

Main Methods:

• DNA sequencing of gamma delta at its native locus on the F factor and at insertion sites in pBR322.
• Sequence analysis to identify flanking DNA and terminal repeats.

Main Results:

• Transposition of gamma delta into pBR322 resulted in a five-base-pair duplication of the target sequence.
• No such duplications were observed at the native F factor locus.
• The terminal 35-base-pair inverted repeat of gamma delta shares sequence similarity with transposon Tn3 and pSC101.
• A conserved heptanucleotide sequence was identified at the termini of gamma delta, Tn3, pSC101, and bacteriophage Mu.

Conclusions:

• Target DNA duplications are not essential for gamma delta transposition and do not direct insertion to homologous sites.
• The conserved heptanucleotide sequence at the termini of gamma delta and other mobile elements may be important for transposition.
• Sequence similarities suggest a common mechanism or evolutionary origin for these mobile elements.