Cloned streptococcal genes encoding protein G and their use to construct recombinant microorganisms to produce protein G

#This present invention relates to the cloning of genes which specify the biosynthesis of Streptococcus Protein G, cloned genes which encode protein G variants having the immunoglobulin binding properties of protein G, and the use of organisms transformed with the cloned genes to produce Protein G and Protein G-like variant polypeptides.

#There has been a growing interest in recent years in bacterial F.sub.c receptors, molecules that bind to antibodies through a nonimmune mechanism. This binding is not to the antigen recognition site, which is located in the F.sub.ab portion of the antibody molecule, but to the F.sub.c portion of the antibody. The F.sub.c region is common to many types of antibodies, thus bacterial F.sub.c receptors can bind to many types of antibodies. This property makes bacterial F.sub.c receptors useful in a number of immunochemical applications.

#Bacterial F.sub.c receptors have a number of useful or potentially useful applications, primarily in the detection of antibodies, the purification of antibodies and the treatment of diseases. The detection of antibodies is required in several phases of laboratory research in immunology, including the screening of hybridoma clones for the secretion of specific monoclonal antibodies, the measurement of the immune response of an immunized animal, and the quantitation of antigens by competitive binding assays. Methods for detecting antibodies using bacterial F.sub.c receptors have been found to be more sensitive and less prone to interference and high background signals than other detection methods [Boyle, M. D. P., Biotechniques 2:334-340 (1984)].

#FIG. 1 is a diagram showing the salient features of plasmid pGX1066, a vector suitable for use in cloning a Protein G-encoding DNA fragment.

#FIG. 2 shows a partial restriction map of plasmid pGX4533, a recombinant plasmid vector containing a Protein G-encoding DNA fragment.

#FIGS. 3 and 3A-C show a DNA sequence for the Protein G gene, as well as the amino acid sequence encoded by the gene.

#The present invention relates to cloned Protein G genes. A DNA fragment comprising a Protein G gene is isolated from a Streptococcus Sp., Lancefield Group G, stain and inserted into a cloning vector. Another aspect of the invention relates to production of Protein G by transforming host cells with a recombinant vector comprising a cloned Protein G gene and culturing the transformed cells under protein-producing conditions, whereupon Protein G is produced by the cells.

#Yet another aspect of the invention is directed to production of a Protein G variant, said variant containing from one to twenty Protein G binding sites per molecule. This Protein G variant has the formula:

#-(-B-b-).sub.n -