Chi-dependent DNA strand cleavage by RecBC enzyme

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Chi sites are known to enhance homologous recombination in E. coli via the RecBC pathway.
• The precise mechanism of Chi site function and its interaction with RecBC enzyme has been inferred genetically.

Purpose of the Study:

• To investigate the direct biochemical interaction between the RecBC enzyme and Chi DNA sequences.
• To elucidate the role of RecBC enzyme in Chi-mediated DNA cleavage and its implications for recombination.

Main Methods:

• Biochemical assays to detect DNA cleavage catalyzed by purified RecBC enzyme.
• Site-directed mutagenesis of the Chi sequence and the recC gene to assess their impact on cleavage activity.

Main Results:

• RecBC enzyme catalyzes Chi-dependent cleavage of one DNA strand at the specific sequence 5'G-C-T-G-G-T-G-G3'.
• Cleavage is sensitive to single base pair changes in the Chi sequence and mutations in the recC gene.
• The reaction produces single-stranded DNA from double-stranded DNA, indicating direct RecBC-Chi interaction.

Conclusions:

• RecBC enzyme directly interacts with Chi sites, mediating sequence-specific DNA cleavage.
• This Chi-specific cleavage is a key step preceding strand exchange in homologous recombination models.
• The findings provide biochemical evidence for the inferred genetic properties of Chi and recBC.