Characterization of immunoglobulin enhancer deletions in murine plasmacytomas

We have analyzed enhancer deletions found in murine plasmacytomas by DNA cloning. This analysis revealed that the deletions occurred between the JH region and the switch region, removing the Ig heavy chain enhancer. The loss of the enhancer did not significantly affect the level of heavy chain expression as determined by RNA blots. Nucleotide sequence analysis revealed that there are no characteristic or homologous sequences around the recombination site. Extra nucleotides were found at the recombination sites, in a manner analogous to Ig and T-cell receptor V-D-J joining. The germline JH and switch sequences involved in the deletion were analyzed by the in vitro DNA cleavage system with an endonucleolytic activity purified from mouse fetal liver nuclear extracts. It was found that the germline JH DNA was strongly cleaved at the deletion recombination site.