Recombination Events near the Immunoglobulin CM Gene Join Variable and Constant Region Genes, Switch Heavy-Chain Expression, or Inactivate the Locus

Abstract

Immunoglobulin heavy-chain expression is initiated by recombination between a variable region (VH) gene and one of several joining region (JH) genes located near the y constant region (CM) gene, and the active VH gene can subsequently switch to another CH gene. That the general mechanism for CH switching involves recombination between sites within the JH-CM intervening sequence and the 5’ flanking region of another CH gene is supported here by Southern blot hybridization analysis of eight IgG- and IgA-secreting plasmacytomas. An alternative model requiring successive VH linkage to similar JH clusters near each CH gene is shown to be very unlikely since the mouse genome appears to contain onl..