Amino acid sequence of the first 217 residues of a mouse heavy chain (MOPC 47A) with a domain deletion.

Cyanogen bromide cleavage of the deleted heavy (alpha) chain of mouse IgA 47A yielded five peptides, CNBr 1-5, consisting of 34, 50, 28, 70, and 160 residues. A 217-residue NH2-terminal sequence, which comprises the variable region and the first domain of the constant region (CH1), and a 19-residue COOH-terminal sequence of the chain were obtained from the sequences of CNBr 1-4 and the NH2-terminal and COOH-terminal sequences of CNBr 5. The tryptic peptides of the remainder of the chain have been partially characterized. Comparison of these data with the sequences of other, nondeleted, chains reveals that the 47A chain terminates exactly at the end of the CH2 domain and that there are no deletions up to that point. It is concluded that the deletion in the chain is a single, large deletion consisting of the entire CH3 domain. The 47A chain also differs from other, nondeleted, mouse alpha chains derived from BALB/c strains in that it contains a labile cysteine at position 135, which is believed to participate in the light-heavy chain bond, and contains galactosamine in the hinge region. This may mean that the 47A alpha chain, in addition to being deleted, represents a mouse IgA subclass analogous to human IgA1.