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Control of V(D)J Recombination through Transcriptional Elongation and Changes in Locus Chromatin Structure and Nuclear Organization
V(D)J recombination is the assembly of gene segments at the antigen receptor loci to
generate antigen receptor diversity in T and B lymphocytes. This process is regulated,
according to defined developmental programs, by the action of a single specific
recombinase complex formed by the recombination antigen gene (RAG-1/2) proteins
that are expressed in immature lymphocytes. V(D)J recombination is strictly controlled
by RAG-1/2 accessibility to specific recombination signal sequences in chromatin at
several levels: cellular lineage, temporal regulation, gene segment order, and allelic
exclusion. DNA cleavage by RAG-1/2 is regulated by the chromatin structure,
transcriptional elongation, and three-dimensional architecture and position of the
antigen receptor loci in the nucleus. Cis-elements specifically direct transcription and
V(D)J recombination at these loci through interactions with transacting factors that form
molecular machines that mediate a sequence of structural events. These events open
chromatin to activate transcriptional elongation and to permit the access of RAG-1/2 to
their recombination signal sequences to drive the juxtaposition of the V, D, and J
segments and the recombination reaction itself. This chapter summarizes the advances
in this area and the important role of the structure and position of antigen receptor loci
within the nucleus to control this process