Nucleotide sequence of the constant region of a chicken mu heavy chain immunoglobulin mRNA.

We have recently reported the sequence of a chicken Ig lambda light chain cDNA clone, isolated from a spleen partial cDNA library (1). In this paper, we describe the characterization of a cDNA clone coding for the chicken constant (C) region of the secreted mu chain. This is the first report on the nucleotide and amino acid sequence of a chicken Ig heavy chain constant region. It contains the 3' untranslated region of the mu mRNA up to the poly(A) tail, and, in comparison with the mouse Cmu sequence, displays the overall domain size and organization of a secreted mu chain, i.e.: a characteristic COOH-terminal region, a Cmu4, a Cmu3, a Cmu2, and part of a Cmu1 domain. The sequence homology between these two species ranges from 45% for the Cmu4 to 18% for the Cmu2. Thus, the Cmu sequence appears much less conserved between chicken and mouse than their respective lambda light chain constant regions (1). These results, together with some distinctive features of the Cmu2 domain, may be of evolutionary relevance and will be further discussed.