Amino acid sequence of a mouse immunoglobulin µ chain
The complete amino acid sequence of the mouse µ chain from the BALB/c myeloma tumor MOPC 104E is reported. The Cµ region contains four consecutive homology regions of approximately 110 residues and a COOH-terminal region of 19 residues. A comparison of this µ chain from mouse with a complete µ sequence from human (Ou) and a partial µ chain sequence from dog (Moo) reveals a striking gradient of increasing homology from the NH2-terminal to the COOH-terminal portion of these µ chains, with the former being the least and the latter the most highly conserved. Four of the five sites of carbohydrate attachment appear to be at identical residue positions when the constant regions of the mouse and human µ chains are compared. The µ chain of MOPC 104E has a carbohydrate moiety attached in the second hypervariable region. This is particularly interesting in view of the fact that MOPC 104E binds α-(1→3)-dextran, a simple carbohydrate. The structural and functional constraints imposed by these comparative sequence analyses are discussed.