Orientational control of fimE expression in Escherichia coli.
Phase-variable expression of type 1 fimbriae is, in part, controlled by site-specific DNA inversion of the fim switch in Escherichia coli. Of the two fim recombinases (FimB and FimE) that catalyse the inversion reaction, FimE exhibits a strong bias for phase switching from the ON to the OFF orientation. The specificity associated with fimE is the result of two different mechanisms: (i) FimE exhibits a preference for the invertible element in the ON orientation as substrate for recombination; (ii) the invertible element in the OFF orientation acts in cis to inhibit recombinase activity (orientational control). We show here that the invertible element negatively regulates fimE, even though expression of a fimE-lacZYA transcriptional fusion is unaffected by orientational control. The fimE transcript extends into the invertible region and hence switch ON-specific and switch OFF-specific mRNA contain different sequences. Furthermore, we show that orientational control is suppressed by the insertion of a structured RNA (tRNA(Gly)) between fimE and the fim switch, indicating that the switch OFF-specific mRNA is inactivated by 3' to 5' degradation. Analysis of the fim switch reveals that it contains two inhibitory elements that exert orientational control independently.
Sohanpal
B K
BK
Research School of Biosciences, University of Kent, Canterbury, Kent, CT2 7NJ, UK.
Kulasekara
H D
HD
Bonnen
A
A
Blomfield
I C
IC
D001426:Bacterial Proteins / Q000235:genetics*; D007446:Chromosome Inversion; D004268:DNA-Binding Proteins / Q000235:genetics*; D004926:Escherichia coli / Q000235:genetics*; D029968:Escherichia coli Proteins; D010861:Fimbriae, Bacterial / Q000235:genetics; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial / Q000235:genetics; D005812:Genes, Switch / Q000235:genetics; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012343:RNA, Transfer / Q000235:genetics / Q000378:metabolism; D011995:Recombination, Genetic / Q000235:genetics*; D014158:Transcription, Genetic / Q000235:genetics
D001426:Bacterial Proteins; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D012333:RNA, Messenger; C081955:fimE protein, E coli; D012343:RNA, Transfer