Structure of the Constant and 3' Untranslated Regions of the Murine γ 2b Heavy Chain Messenger RNA

The complete coding sequence for the constant region of the mouse γ 2b immunoglobulin heavy chain and the 3' untranslated region has been determined. The coding portion of the sequence is 1008 nucleotides long (amino acid residues 114 to 449), and the 3' noncoding region contains 102 nucleotides preceeding the polyadenylate. An extra carboxyl-terminal lysine residue which had not been observed in the γ 2b or other γ subclass protein sequences occurs in the nucleotide sequence and is probably processed posttranslationally. A 17-nucleotide sequence occurs with slight variation twice in C_H1 and once in C_H2 domains in the same relative location but with different translational phase. This sequence may be the site of crossover in a γ 2b \cdot \ γ 2a heavy chain variant, an indication of possible recombinational activity of some kind.