Protein FimH is an adhesive terminal subunit of Escherichia coli type I pili. The content of FimH on the surface of a bacterial cell does not directly depend on FimH expression, but is limited by expression of other fim cluster genes encoding structural subunits and proteins responsible for assembly of pili. Piline domain, a component of FimH, cannot incorporate into the fimbria independently, without lectin domain. It seems that fimbriae containing only piline domain are not formed because of inability of the piline domain to initiate the process of assembly. © Springer Science+Business Media, Inc. 2006.