Study on the genetic determinants responsible for expression and assembly of CS3 fimbriae

Colonization factor antigens (CFAs) are important virulent factors and protective antigens of enterotoxigenic Escherichia coli (ETEC). Among the known CFAs of human origin, CS3 is a major fimbriae antigen. To study the genes associated with the expression and assembly of CS3 is a key step to delineate the regulating mechanism of expression and assembly of the fimbriae. In this paper we analyzed the restriction map of the CS3 genetic determinant and successfully cloned the CS3 subunit gene and the region encoding the auxiliary proteins. Expression results of the recombinant plasmids in minicells showed that the genetic determinant of CS3 fimbriae encodes six polypeptides with molecular weights 15, 17, 24, 27, 48, and 90 kDa. Western blotting and complementary expression analysis among the different mutants showed that the 15 kDa/17 kDa proteins compose the CS3 subunit and the 17 kDa protein is the precursor. The others may be necessary for the assembly of CS3 fimbriae. The relative locations of various genes of the CS3 genetic determinant were also determined.