Nucleotide Composition of Human Ig Nontemplated Regions Depends on Trimming of the Flanking Gene Segments, and Terminal Deoxynucleotidyl Transferase Favors Adding Cytosine, Not Guanosine, in Most VDJ Rearrangements

J Immunol. 2018 Sep 15;201(6):1765-1774. doi: 10.4049/jimmunol.1800100. Epub 2018 Aug 10.


The formation of nontemplated (N) regions during Ig gene rearrangement is a major contributor to Ab diversity. To gain insights into the mechanisms behind this, we studied the nucleotide composition of N regions within 29,962 unique human VHDJH rearrangements and 8728 unique human DJH rearrangements containing exactly one identifiable D gene segment and thus two N regions, N1 and N2. We found a distinct decreasing content of cytosine (C) and increasing content of guanine (G) across each N region, suggesting that N regions are typically generated by concatenation of two 3' overhangs synthesized by addition of nucleoside triphosphates with a preference for dCTP. This challenges the general assumption that the terminal deoxynucleotidyl transferase favors dGTP in vivo. Furthermore, we found that the G and C gradients depended strongly on whether the germline gene segments were trimmed or not. Our data show that C-enriched N addition preferentially happens at trimmed 3' ends of VH, D, and JH gene segments, indicating a dependency of the transferase mechanism upon the nuclease mechanism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Child
  • Child, Preschool
  • Cytosine / immunology
  • DNA Nucleotidylexotransferase / genetics
  • DNA Nucleotidylexotransferase / immunology*
  • Female
  • Gene Rearrangement, B-Lymphocyte, Heavy Chain*
  • Guanosine / genetics
  • Guanosine / immunology
  • Humans
  • Immunoglobulin Heavy Chains* / genetics
  • Immunoglobulin Heavy Chains* / immunology
  • Immunoglobulin Variable Region* / genetics
  • Immunoglobulin Variable Region* / immunology
  • Male


  • Immunoglobulin Heavy Chains
  • Immunoglobulin Variable Region
  • Guanosine
  • Cytosine
  • DNA Nucleotidylexotransferase