Hypermutation targets a green fluorescent protein-encoding transgene in the presence of immunoglobulin enhancers

Hypermutation introduces point mutations into the gene segments encoding immunoglobulin variable regions at a rate that is a million-fold higher than the spontaneous mutation rate in most of the genome. Because Ig enhancers are required to target hypermutation, transcription appears to play a critical role for the hypermutation mechanism. We have developed a novel system for detecting mutations that enables us to determine the influence of expression levels on the mutability of a transgene. This system utilizes a green fluorescent protein receptor gene and the powerful enumeration and quantification properties of flow cytometry. We have tested this system with several constructs bearing Ig enhancers in cell lines with active and inactive hypermutation systems.