mRNA for surface immunoglobulin γ chains encodes a highly conserved transmembrane sequence and a 28-residue intracellular domain

Abstract

To probe the structure of the γ heavy chain of membrane IgG and the mRNA and gene segments that encode it, we have analyzed cDNA clones derived from a γ1 membrane RNA of B lymphoma 2PK-3. The nucleotide sequence of the clones indicated that membrane γ1 chains bear a COOH-terminal 71-residue segment that is absent from secretory γ1 chains. This terminus includes a 26-residue hydrophobic transmembrane region homologous to that of membrane μ chains, significantly, a 28-residue intracellular domain found only on γ chains. The extra domain suggests that receptor IgG, on memory B cells, may generate a different signal on binding antigen than does receptor IgM, on virgin B cells. The γ1 membrane te..