Within the 162 bp L region is a short coding region for a 14 aa peptide called the leader peptide. Two trp codons are present at 10th and 11th positions. Normally when the final codon of the leader peptide is translated the ribosome partially covers 1 and 2 so they can not pair. This allows 3-4 to pair causing transcription termination. Therefore 3-4 can not form and transcription continues.
Some regulators are specific, bind only to one location.
Some are more general, Bind many places. Lex A is a general negative regulator of genes encoding DNA repair induced from UV light. If too much CRP is present it will bind to its own promoter and inhibit transcription. Expression level is controlled by the strength of the promoter. Ribosome binding disassociation efficiencies.