Before revision: The fim switch in Escherichia coli is the mechanism by which the fim gene cluster, encoding Type I Pili, is transcriptionally controlled.
After revision: The fim switch in Escherichia coli is A PIECE OF DNA OF 314 BP LONG WHOSE ORIENTATION DETERMINES EITHER THE TRANSCRIPTION OR REPRESSION OF THE STRUCTURAL GENES OF THE fim gene cluster, encoding Type I Pili, is transcriptionally controlled.