Complete nucleotide sequence of immunoglobulin γ2b chain gene cloned from newborn mouse DNA

Abstract

Immunoglobulin γheavy chain protein comprises five classes μ, γ, α, δ and ɛ chains which differ in amino acid sequences of the constant (C) region. The γ heavy chain class, which contains three domains and the hinge region, is divided into several subclasses such as γ1, γ2a, γ2b and γ3 in mouse. Amino acid sequence studies of mouse and human heavy chain proteins have shown that the γ subclass heavy chains are more closely related to each other than to the heavy chains of other classes. A similar conclusion was drawn from a nucleic acid hybridisation study using cDNAs complementary to the purified heavy chain mRNAs of the γ subclasses¹. These results suggest that the immunoglobulin heavy chain genes of the γ subclasses have evolved by relatively recent gene duplication of the ancestral γ chain gene. The complete nucleotide sequence of the γ1 chain gene has demonstrated unequivocally that the domains and the hinge region are encoded in separate segments of DNA². Partial nucleotide sequences of the γ2b chain gene indicated that the γ2b gene is interrupted by intervening sequences (IS) at locations homologous to those in the γ1 chain gene³. Comparison of the structures of these closely related genes would give new insights into evolution of eukaryotic genes and serve for understanding biological significance of various segments of the genes. We have now determined the complete nucleotide sequence of the immunoglobulin γ2b chain gene cloned from newborn mouse DNA. The sequence not only predicts the complete amino acid sequence of the γ2b chain but also demonstrates that the γ2b chain gene is interrupted by three intervening sequences at the junction of the domains and the hinge region.