Junctional diversity

Junctional diversity describes the DNA sequence variations introduced by the improper joining of gene segments during the process of V(D)J recombination.

This process of V(D)J recombination has vital roles for the vertebrate immune system, as it is able to generate a huge repertoire of different T-cell receptor (TCR) and immunoglobulin molecules required for pathogen antigen recognition by T-cells and B cells, respectively.

This joining is a very inaccurate process that results in the variable addition or subtraction of nucleotides and, thus, generates junctional diversity.

Subsequent to this, the enzyme, terminal deoxynucleotidyl transferase (TdT), adds further random 'N' nucleotides.

Exonucleases remove these unpaired nucleotides and the gaps are filled by DNA synthesis and repair machinery.

Generation of junctional diversity through recombination illustrated between two gene segments: D (blue) and J (green). Sections highlighted in red show nucleotides added at each stage.