Complete amino acid sequence of a mouse immunoglobulin alpha chain (MOPC 511).

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Abstract
The complete amino acid sequence of the 432-residue H (.alpha.) chain of mouse myeloma MOPC511 was determined. The variable region of the .alpha. chain of IgA 511, a phosphocholine-binding protein, is highly homologous to that of the other phosphocholine-binding immunoglobulins. Comparison of the 511 .alpha. chain constant region with that of other mouse and human H chains shows that sequence divergences and deletions are more extensive within domain disulfide bridges than in other parts of a domain. The CH3 domain disulfide bridge of the 511 .alpha. chain, for example, consists of only 28 amino acid residues compared to 60 residues for other chains and domains. Sequence divergences are also apparent at the CH2/CH3 domain boundary, an area where a number of frameshift mutations have occurred. One mutant, mouse IgA 47A, lacks the entire CH3 domain. Comparison of the 511 .alpha. chain with the 47A .alpha. chain reveals 2 nonconservative amino acid changes at the COOH terminus of the 47A chain, Ser-Gln for Val-Thr in the 511 chain. These changes and the deletion of the CH3 domain can be explained by a single genetic event.sbd.namely, a frameshift mutation followed by premature chain termination. The remainder of the 47A constant region, including the hinge region, is identical to the 511 .alpha. chain, except for 2 conservative changes in the CH1 domain: serine-126 and threonine-197 in the 511 .alpha. chain are both replaced by alanine in the 47A chain.