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. Author manuscript; available in PMC: 2016 Jul 1.
Published in final edited form as: Cell Immunol. 2015 May 1;296(1):87–94. doi: 10.1016/j.cellimm.2015.04.007

Figure 3.

Figure 3

Schematic diagram of an VLR gene and the postulated assembly mechanism. (A) Domain organisation of a functional VLR protein. The diversity region is composed of a 3'-end of the N-terminal LRR (LRRNT), LRR1, multiple LRRVs, connecting peptide (CP) and a 5'-end of the C-terminal LRR (LRRCT). (B) Hypothetical scheme of VLR gene assembly process. Multiple LRR cassettes are located upstream and downstream of a pre-assembled germline VLR gene with its non-coding intervening sequence. At the beginning of the gene assembly process, a cytosine deaminase (CDA) converts cytosine (C) to uracil (U) in the germline VLR gene. The uracil is then removed by uracil-DNA glycosylase (UNG), leaving an apurinic (AP) site, blank residue in DNA. The AP site activates nicking activity of AP endonuclease (APE) which leads to a DNA double strand break. To repair this break, homologous recombination starts from the 5'-end and/or 3'-end of the break, based on the sequence homology of 10-30bp between the donor and acceptor LRR cassettes. This process is repeated along with deletion of the intervening sequence until a functional VLR is expressed on the cell surface.