Which process is right to describe V(D)J recombination? RAG-1 and RSS recurring process
Excerpt from Cellular and Molecular Immunology, 8th ED, p.181-182. Don't up-vote me, i just thought this text offers a good, up-to-date explanation.


  The Mechanism of V(D)J Recombination
  
  Rearrangement of Ig and TCR genes represents a special kind of non-homologous DNA recombination 
  event, mediated by the coordinated activities of several 
  enzymes, some of which are found only in developing 
  lymphocytes, whereas others are ubiquitous DNA double-stranded break repair (DSBR) enzymes.Although 
  the mechanism of V(D)J recombination is fairly well 
  understood and will be described here, how exactly 
  specific loci are made accessible to the machinery 
  involved in recombination remains to be determined. 
  It is likely that the accessibility of the Ig and TCR loci to 
  the enzymes that mediate recombination is regulated 
  in developing B and T cells by several mechanisms, 
  including epigenetic alterations in chromatin structure 
  and DNA as discussed earlier, and basal transcriptional 
  activity in the gene loci.
  The process of V(D)J recombination can be divided 
  into four distinct events that flow sequentially from one 
  to the next (Fig. 8-10):
  
  1. Synapsis: Portions of the chromosome on which the 
  antigen receptor gene is located are made accessible 
  to the recombination machinery. Two selected coding segments and their adjacent RSSs are brought 
  together by a chromosomal looping event and held 
  in position for subsequent cleavage, processing, and 
  joining.
  
  2. Cleavage: Double-stranded breaks are enzymatically generated at RSS-coding sequence junctions 
  by machinery that is lymphoid specific. Two proteins encoded by lymphoid-specific genes, called 
  recombination-activating gene 1and recombination-activating gene 2(RAG1and RAG2), form 
  a  complex, containing two molecules of each protein, 
  that plays an essential role in V(D)J recombination. 
  The Rag-1/Rag-2complex is also known as the V(D)J 
  recombinase.The Rag-1 protein, in a manner similar to a restriction endonuclease, recognizes the DNA 
  sequence at the junction between a heptamer and a 
  coding segment and cleaves it, but it is enzymatically 
  active only when complexed with the Rag-2 protein. 
  The Rag-2 protein may help link the Rag-1/Rag-2 tetramer to other proteins, including accessibility factors that bring these proteins to specific open receptor 
  gene loci at specific times and at defined stages of lymphocyte development. Rag-1 and Rag-2 contribute to 
  holding together gene segments during the process of 
  chromosomal folding or synapsis. Rag-1 then makes 
  a nick (on one DNA strand) between the coding end 
  and the heptamer. The released 3′OH of the coding 
  end then attacks a phosphodiester bond on the other 
  DNA strand, forming a covalent hairpin. The signal 
  end (including the heptamer and the rest of the RSS) 
  does not form a hairpin and is generated as a blunt 
  double-stranded DNA terminus that undergoes no 
  further processing. This double-stranded break results 
  in a closed hairpin of one coding segment being held 
  in apposition to the closed hairpin of the other coding end and two blunt recombination signal ends being placed next to each other. Rag-1 and Rag-2, apart 
  from generating the double-stranded breaks, also hold 
  the hairpin ends and the blunt ends together before 
  the modification of the coding ends and the process of 
  ligation.
  
  RAGgenes are lymphoid specific and are expressed 
  only in developing B and T cells. Rag proteins are 
  expressed mainly in the G0and G1
  stages of the cell 
  cycle and are inactivated in proliferating cells. It is 
  thought that limiting DNA cleavage and recombination 
  to the G
  0 and G1
  stages minimizes the risk of generating inappropriate DNA breaks during DNA replication or during mitosis. Mice without functional Rag1
  or Rag2genes (Ragknockout mice) fail to develop B or 
  T lymphocytes, and Rag-1 or Rag-2 deficiency is also 
  a rare cause of SCID, in which patients also lack all 
  lymphocytes.
  
  3. Hairpin opening and end-processing: The broken 
  coding ends are modified by the addition or removal 
  of bases, and thus greater diversity is generated. After the formation of double-stranded breaks, hairpins must be resolved (opened up) at the coding 
  junctions, and bases may be added to or removed 
  from the coding ends to ensure even greater diversification. Artemisis an endonuclease that opens 
  up the hairpins at the coding ends. In the absence 
  of Artemis, hairpins cannot be opened, and mature 
  T and B cells cannot be generated. Mutations in 
  ARTEMIS are a rare cause of SCID, similar to patients with RAG1or RAG2mutations. (see Chapter 
  21). A lymphoid-specific enzyme, called terminal 
  deoxynucleotidyl transferase (TdT), adds bases to 
  broken DNA ends and will be discussed later in the 
  chapter in the context of junctional diversity.
  
  4. Joining: The broken coding ends as well as the signal ends are brought together and ligated by a double-stranded break repair process found in all cells 
  that is called nonhomologous end joining. A number 
  of ubiquitous factors participate in nonhomologous 
  end joining. Ku70 and Ku80 are DNA end-binding 
  proteins that bind to the breaks and recruit the catalytic subunit of DNA-dependent protein kinase 
  (DNA-PK), a double-stranded DNA repair enzyme. 
  This enzyme is defective in mice carrying the severe 
  combined immunodeficiency (scid)mutation, and mutations in the gene encoding this enzyme have also 
  been discovered in human SCID patients (see Chapter 
  21). Like Rag-deficient mice, scidmice fail to produce 
  mature lymphocytes. DNA-PK also phosphorylates 
  and activates Artemis, which, as mentioned before, is 
  involved in end processing. Ligation of the processed 
  broken ends is mediated by DNA ligase IV and XRCC4, 
  the latter being a non-catalytic but essential subunit of 
  the ligase.




Figure 8-10, Cellular and Molecular Immunology, 8e, p182.