Sensing homology at the strand-swapping step in lambda excisive recombination

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Site-specific recombination is a crucial DNA process.
• Sequence homology plays a role in recombination steps like strand swapping, ligation, and isomerization.
• Understanding homology's precise role is key to dissecting recombination mechanisms.

Purpose of the Study:

• To investigate how sequence homology influences individual steps of lambda site-specific recombination.
• To differentiate the roles of homology in strand transfer versus ligation.
• To determine the minimal homology required for efficient recombination.

Main Methods:

• Utilized half-att site suicide substrates to isolate and study single and double top-strand transfers.
• Analyzed the formation and resolution of covalent three-way DNA junctions.
• Varied nucleotide pairing to assess homology dependence at different stages.

Main Results:

• Both the rate and efficiency of Y-junction formation are homology-dependent.
• Three nucleotides of homology, in either forward or contrary alignment, maximize strand swapping stability.
• Homology adjacent to one site enhances strand transfer at a mismatched site.
• Homology also stimulates ligation and stabilizes recombination products.

Conclusions:

• Homology is sensed during the strand-swapping step, prior to ligation.
• Double-strand transfer, not single-strand transfer, confers stability to the recombination intermediate.
• Homology is critical for multiple steps in site-specific recombination, influencing both initial exchange and final product stability.