16.2.3 Hairpin-opening and processing of ends

The broken ends are modified by addition or deletion of the base pairs to produce maximum diversity among the sequences. Artemis an endonuclease opens up the hairpin for any further modification. Another unique enzyme called terminal deoxynucleotide transferase (TdT) helps to add the nucleotide sequence in the 3' end of the broken region that again is responsible for the maximum diversity. Nucleotides may be added to asymmetrically cleaved hairpin structure in a template manner those nucleotides are called P sequences . Nucleotides may be added to the recombination site in a nontemplated manner by TdT enzyme; those are referred as N sequences.  

16.2.4 Joining

The broken ends are joined by double stranded repair process. DNA end-binding proteins Ku70 and Ku80 are involved in recruiting protein kinase which helps in the ligation of broken ends and are carried out by DNA ligase.

Figure 16.2 Different events during V(D)J recombination: