Amino-Acid Sequence of the Variable Region of the Heavy (Alpha) Chain of a Mouse Myeloma Protein with Anti-Hapten Activity

Cyanogen bromide cleavage of the heavy (alpha) chain of protein 315 (an immunoglobulin A mouse myeloma protein with anti-dinitrophenyl activity) yielded five fragments of which one (CN2), with 156 residues, contained the chain's entire variable region. Determination of the amino-acid sequence of CN2 showed that: (1) the variable region has appreciable homology (about 33% identities) with the variable region of the light chain from the same molecule; and (2) the constant-region sequence immediately following the probable transition from variable to constant domains is the same in the protein-315 α as in human γ 1 and μ chains (-Val-Ser-Ser-). The sequence of the cyanogen bromide octapeptide (CN5) from the carboxy terminus of the protein-315 heavy chain closely resembles the corresponding segments of human α and μ chains.