Structural and functional characterization of IS679 and IS66-family elements.

Area of Science:

• Molecular Biology
• Genetics
• Microbiology

Background:

• Insertion sequence (IS) elements are mobile genetic elements found in bacteria.
• Understanding IS element transposition is crucial for studying genome dynamics and gene regulation.

Purpose of the Study:

• To characterize a newly identified insertion sequence element, IS679, from enteropathogenic Escherichia coli.
• To elucidate the transposition mechanism and genetic requirements of IS679.

Main Methods:

• Identification and characterization of IS679 in plasmid pB171.
• Construction of a composite transposon (Tn679) for transposition assays.
• Transposition assays using a mating system and analysis of target site duplication.
• Homology searches to identify related elements in other bacterial species.

Main Results:

• IS679, a 2,704 bp IS element with imperfect terminal inverted repeats (IRs), was identified.
• Tn679, containing a kanamycin resistance gene flanked by IS679 elements, transposed at high frequency, duplicating an 8-bp target sequence.
• All three open reading frames (ORFs) of IS679 (tnpA, tnpB, tnpC) were found to be essential for transposition.
• Homologous elements belonging to the IS66 family are widespread in Gram-negative bacteria, including Agrobacterium, Rhizobium, Pseudomonas, and Vibrio species.

Conclusions:

• IS679 is a functional insertion sequence element belonging to the IS66 family.
• Transposition of IS679 requires all three ORFs and results in 8-bp target site duplication.
• The widespread distribution of IS679-like elements highlights their significant role in bacterial genome evolution.