Comparative study of class 1 integron and Vibrio cholerae superintegron integrase activities

Area of Science:

• Microbiology
• Molecular Biology
• Genetics

Background:

• Superintegrons (SIs) and multiresistant integrons (MRIs) differ structurally, with SIs being sedentary and MRIs mobile, and having homogeneous vs. variable attC sites, respectively.
• The functional implications of these attC site differences on recombination activity remain largely unexplored.

Purpose of the Study:

• To compare the recombination activities of the Vibrio cholerae SI integrase (VchIntIA) and the class 1 MRI integrase (IntI1).
• To investigate if the variability in attC sites correlates with differences in integrase recombination efficiency and substrate specificity.

Main Methods:

• Development of two assays to measure cassette deletion and integration frequencies at attI sites.
• Comparative analysis of VchIntIA and IntI1 recombination activity across various attC sites.
• Site-directed mutagenesis of V. cholerae repeats (VCRs) to map key recombination positions.
• Cointegration assays in both E. coli and V. cholerae to quantify recombination efficiencies.

Main Results:

• VchIntIA recombined a narrower range of attC sites compared to IntI1.
• Mutations in VCRs differentially affected VchIntIA and IntI1 activities.
• IntI1-mediated recombination was significantly more efficient than VchIntIA-mediated recombination in E. coli.
• VchIntIA-mediated recombination was significantly more efficient in V. cholerae than in E. coli.

Conclusions:

• The substrate recognition and recombination reactions mediated by VchIntIA in SIs differ from the class 1 MRI paradigm.
• The attC site variability in MRIs may contribute to their broader substrate acceptance compared to SIs.