The uropathogenic Escherichia coli KS52 strain expresses a mannose-resistant hemagglutinin AFA-I, which recognizes a human erythrocyte site distinct from the alpha-digalactoside glycosphingolipid receptor common to uropathogenic E. coli strains specifying a P adhesin. A 6.7-kilobase chromosomal DNA fragment was cloned from KS52 into pBR322 and was shown to be necessary for host cell mannose-resistant hemagglutination expression and uroepithelial cell adherence (Labigne-Roussel et al., Infect. Immun. 46:251-259, 1984). The genetic organization of the 6.7-kilobase DNA fragment was investigated by generating derivative plasmids, and the polypeptides encoded by those plasmids in isolated minicells were analyzed on polyacrylamide gel. The 6.7-kilobase insert expresses five polypeptides of molecular mass 13,000, 16,000, 18,500, 30,000, and 100,000 daltons encoded, respectively, by the afaA, afaE, afaD, afaB, and afaC genes. The five genes were localized and were shown to belong to the same transcriptional unit. The afaB, afaC, and afaE gene products are required for mannose-resistant hemagglutination expression, whereas mutations in or deletions of either afaA or afaD do not modify host mannose-resistant hemagglutination expression. The afaE gene was identified as the structural gene encoding hemagglutinin. The gene has been sequenced; it encodes a 152-residue protein containing a typical 21-residue procaryote signal sequence and a 131-residue mature polypeptide, the AFA-I adhesin.