Comparison of mouse immunoglobulin gamma 2a and gamma 2b chain genes suggests that exons can be exchanged between genes in a multigenic family.

Abstract

A 23-kilobase EcoRI DNA fragment coding for the BALB/c Ig .gamma.2a chain was cloned from mouse embryo DNA in the cosmid pJC74, and a nucleotide sequence of 1904 bases was determined for the entire constant region (CH1, CH2 and CH3), the 3 intervening sequences (IVS 1, IVS 2 and IVS 3) and the 5'' and 3'' flanking sequences. When the .gamma.2a chain nucleotide sequence was compared with the .gamma.2b chain nucleotide sequence, the % homology of corresponding segments (excluding deletion and insertion) was 82% for the 5'' flanking sequence, 87% for CH1, 84% for IVS 1, 96% for the hinge, 95% for IVS 2, 94.6% for CH2, 86% for IVS 3, 74% for CH3, 89% for the 3'' untranslated region and 92% for the 3'' flanking region. Different domains of .gamma.2a and .gamma.2b evidently have independent rates of evolution and some of the noncoding segments of the gene are more conserved than are adjacent coding segments. Hypotheses on the possible role of IVS in gene evolution and expression are discussed.