Cell surface proteins of a group A streptococcus type M4: the IgA receptor and a receptor related to M proteins are coded for by closely linked genes.

Two genes coding for cell surface proteins were cloned from a group A streptococcus type M4: the gene for an IgA binding protein and the gene for a fibrinogen binding protein. Both proteins were purified and partially characterized after expression in Escherichia coli. There was no immunological cross-reaction between the two proteins. The IgA binding protein, called protein Arp4, is similar to an IgA receptor previously purified from another strain of group A streptococci, but the proteins are not identical. Characterization of many independent clones showed that the two proteins described here are coded for by closely linked genes. Bacterial mutants have been found which have simultaneously lost the ability to express both genes, and a simple method to isolate such mutants is described. The existence of these variants indicates that expression of the two cell surface proteins may be coordinately regulated. Binding of fibrinogen is a characteristic property of streptococcal M proteins, and the available evidence suggests that the fibrinogen binding protein is indeed an M protein.