Recombination between short DNA homologies causes tandem duplication

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• The ampC gene in Escherichia coli K-12 encodes a beta-lactamase enzyme.
• This enzyme hydrolyzes the beta-lactam ring of ampicillin, conferring resistance.
• Ampicillin resistance is directly correlated with the copy number of the ampC gene.

Purpose of the Study:

• To investigate the mechanism of generating multiple ampC gene copies.
• To analyze the DNA sequences involved in the formation of ampC repeats.
• To understand the genetic basis of ampicillin resistance in Escherichia coli.

Main Methods:

• Isolation of ampicillin-resistant mutants with multiple ampC repeats.
• Cloning of a chromosomal DNA segment containing ampC repeats onto a plasmid.
• Nucleotide sequence comparison of DNA regions joining repeat units.

Main Results:

• Isolated ampicillin-resistant mutants with amplified ampC genes.
• Identified that fusions between repeat units occurred within a 12-base pair (bp) sequence of perfect homology.
• Demonstrated a correlation between ampC gene copy number and ampicillin resistance.

Conclusions:

• Recombination between short homologous sequences (12-13 bp) is a potential mechanism for generating tandem duplications.
• This mechanism can lead to the amplification of genes like ampC.
• Understanding this process is crucial for studying antibiotic resistance development.