Evidence for gene conversion among immunoglobulin heavy chain variable region genes

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• The VH (variable heavy) region amino acid sequence of the phosphocholine (PC)-binding hybridoma antibody HP101 6G6 (6G6) from CBA/J mice exhibits significant divergence from other PC-binding antibodies.
• This unique sequence suggests derivation from a gene homologous to the BALB/c V11 gene, a member of the PC VH (T15 VH) gene family not typically utilized for PC-binding antibodies.

Purpose of the Study:

• To determine the nucleic acid sequence of the rearranged VH gene in hybridoma 6G6.
• To investigate the proposed gene conversion mechanism involving multiple PC VH gene family members in the generation of the 6G6 VH gene.

Main Methods:

• Nucleic acid sequencing of the rearranged VH gene of hybridoma 6G6.
• Analysis of 5' noncoding region sequences.
• Southern blot analysis using probes from coding and 5' noncoding regions.

Main Results:

• The nucleic acid sequence of the 6G6 VH gene supports the gene conversion hypothesis by confirming differences relative to the BALB/c V11 gene, including those encoded by other family members.
• Three silent base pair substitutions were identified, further strengthening the correlation with gene conversion.
• Southern blot and sequence data indicate the 6G6 VH gene likely originates from the V11 homologue in CBA/J mice.
• Evidence suggests the presence of all three proposed gene conversion participants within the CBA/J genome.

Conclusions:

• The findings strongly support the hypothesis that the 6G6 VH gene arose through a gene conversion process involving at least three genes from the PC VH gene family.
• The study confirms the origin of the 6G6 VH gene from the V11 homologue in CBA/J mice.
• The presence of the necessary gene family members in the CBA/J genome provides a genetic basis for this gene conversion event.