A silent regulatory gene cfaD' on region 1 of the CFA/I plasmid NTP 113 of enterotoxigenic Escherichia coli.

A DNA sequence, homologous to the cfaD gene of CFA/I region 2, was identified on CFA/I region 1. This sequence is designated cfaD'. It differs from the cfaD gene in containing two deletions and a stop codon. The cfaD' sequence therefore can only encode a truncated CfaD-like protein. The CfaD protein may be a DNA binding protein and functions as a positive regulator of CFA/I fimbriae expression. A regulatory function for the cfaD' is not likely since deletion of the cfaD' sequence does not affect production of CFA/I fimbriae in E. coli K-12 strains. That the cfaD' sequence is present on CFA/I wild-type plasmids isolated from CFA/I strains of different serotypes, obtained at various geographical locations, suggests, however, that this DNA region is not completely without a function.