The nucleotide sequences of the genes faeF, faeH, faeI, and faeJ encoding K88 minor fimbrial subunits were determined. Analysis of the primary structure of the gene products revealed that all four proteins are synthesized with an amino-terminal signal sequence. The molecular masses of the mature FaeF, FaeH, FaeI, and FaeJ proteins were calculated to be 15,161, 25,461, 24,804, and 25,093 Da, respectively. FaeH, FaeI, and FaeJ showed significant homology with FaeG, the major fimbrial subunit of K88 fimbriae. Mutations in the respective genes were constructed. Analysis of the mutants showed that the minor fimbrial subunits FaeF and FaeH play an essential role in the biogenesis but not in the adhesive properties of the K88 fimbriae. Mutations in faeI or faeJ had no significant effect on K88 production or adhesive capacity. Specific antisera against FaeF and FaeH were raised by immunization with hybrid Cro-LacZ-FaeF and Cro-LacZ-FaeH proteins. Immunoblotting and immunoelectron microscopy revealed that FaeF and FaeH are located in or along the K88 fimbrial structure.