A cloned cDNA probe for rat immunoglobulin epsilon heavy chain: construction, identification, and DNA sequence

IgE has clinical importance because it is responsible for immediate hypersensitivity. Studies of IgE expression in rats appear to contradict current models for immunoglobulin gene expression. To study rat IgE expression at the RNA and DNA levels, we have constructed a cDNA for part of the rat epsilon (epsilon) heavy chain that is expressed by a rat myeloma, IR162. The rat epsilon-chain clone was initially identified by an efficient selection scheme. DNA sequencing of the 580-bp cDNA revealed that it encoded 176 amino acids that were 50% homologous to the human epsilon H chain. The sequence begins near the end of the CH2 domain and ends 31 amino acids into the CH4 domain. Cysteines important for the structure of the human IgE were conserved in the rat epsilon H-chain. The identity of the cloned epsilon cDNA was confirmed by comparison with a portion of the constant region gene for mouse epsilon H chain. The mouse and rat nucleotide sequences were 79% homologous.