k Chain variable regions from three galactan binding myeloma proteins.

A series of seven BALB/c myeloma proteins has been identified with binding specificity for antigens containing beta(1 leads to 6)-D-galactopyranosyl moieties. We have determined the primary amino acid sequence of the first 108 residues from the light chains of three of these proteins. The framework portions of the variable regions of these three light chains are identical with residue 100 at which position three different amino acids are found in the three chains. An additional interchange was found at position 106 in one of the proteins. Based on recent DNA sequence studies suggesting that the variable region ends at residue 97, these substitutions indicate the possible existance of multiple genes coding for the region beginning at residue 98 and continuing toward the carboxy terminus. A single amino acid interchange was observed in complementarity determining regions occurring in L3. This substitution (Ile-Trp) would require changes in all three codon bases to produce the respective amino acids if one were derived from the other. Two of these chains are thus indistinguishable for their first 100 amino acids and are the first pair of k chains to exhibit complete identity over their variable regions.