Structure-function analysis of the Fim-B and Fim-E site-specific recombinases of Escherichia coli K-12

Abstract

Phase variable expression of type 1 fimbriae in Escherichia coli arises from a site-specific recombination event that inverts a 314 bp segment of chromosomal DNA (fimS) carrying the promoter for transcription of the gene encoding the fimbrial subunit protein. Two integrase-like recombinases that are 48% identical are involved in switching. The FimB recombinase inverts the switch in either orientation, whereas the FimE protein inverts it predominantly in the ON-to-OFF direction. The FimB and FimE recom binases recognise core-binding sequences at either end of fimS. Inversion of fimS involves site-specific recom bination reaction between two 9 bp inverted repeats that for part of the core binding sequences.