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 alpha as in human gamma1 and mu 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 alpha and mu chains.