Cloning and expression of the gene for an immunoglobulin G Fc receptor protein from a group A streptococcus.

DNA containing the 5' end of the M-12 structural gene was used as a probe in colony hybridizations in an attempt to clone the M-76 gene from an M-type 76 group A streptococcal strain. A single positive colony was detected, and Southern hybridization analysis of plasmid DNA isolated from this colony indicated that the insert DNA had homology to the 5' end of the M-12 structural gene. Subclones were constructed to define the limits of the M-76 gene, and sonicates of these subclones were reacted with M-76-specific antiserum in immunodiffusion. A sonicate of one subclone, JM83(pDH56), reacted strongly with the M-76-specific antiserum but also reacted with preimmune rabbit serum. Protein expressed from this subclone bound immunoglobulin from horse and pig, as well as human myeloma immunoglobulin G (IgG) representing all four subclasses and purified human IgG Fc fragments. This indicated that JM83(pDH56) expressed a protein with characteristics previously attributed to the IgG Fc receptor protein from group A streptococci. Western blot analysis indicated that the cloned IgG Fc receptor protein had a molecular weight of approximately 29,000. Binding studies showed that the Fc receptor gene is expressed by the M-type 76 strain from which it was cloned and by an M- variant.