Mechanistic basis for coding end sequence effects in the initiation of V(D)J recombination

Area of Science:

• Molecular Biology
• Immunology
• Genetics

Background:

• V(D)J recombination is a crucial process for adaptive immune system development.
• Recombination signal sequences (RSS) guide V(D)J recombination.
• The flanking coding end sequence's influence on recombination frequency in vivo is known but mechanistically unclear.

Purpose of the Study:

• To investigate the in vitro effect of coding end sequences on V(D)J recombination.
• To determine which biochemical step of RAG-mediated cleavage is affected by coding end sequences.
• To elucidate the role of coding end sequences in the coordination of 12- and 23-RSS interactions.

Main Methods:

• In vitro biochemical assays using purified RAG proteins.
• Cleavage assays with substrates containing varying coding end sequences.
• Analysis of nicking and hairpin formation steps.
• Experiments involving both 12- and 23-RSS substrates.

Main Results:

• The coding end sequence effect on V(D)J recombination can be recapitulated in vitro.
• Coding end sequences specifically influence the initial nicking step, not subsequent hairpin formation.
• Prenicking the substrate ablates the coding end sequence effect, confirming its specificity to nicking.
• Suboptimal coding end sequences on one RSS can slow hairpin formation at a partner RSS, indicating inter-signal coordination.

Conclusions:

• The coding end sequence is a critical determinant of the nicking step efficiency in V(D)J recombination.
• The observed effects explain how nicking or hairpin formation can be rate-limiting depending on coding end sequence and substrate pairing.
• This study provides a mechanistic understanding of coding end sequence influence on V(D)J recombination initiation and coordination.