How does RNA leader sequence affect Trp operon syst

The base pairing of complementary regions of RNA leader sequence determines if the transcription will be attenuated at the end of leader sequence or will continue for structural genes.

Explanation:

The RNA leader sequence of trp operon is the site where the transcription is initiated.

When tryptophan levels are high, translation of sequence 1 of the leader sequence is followed by base pairing between the complementary 3 and 4 regions of the leader sequence. The base pairing forms a terminator like attenuator and stops the expression of structural genes.

When tryptophan is not present, ribosome pauses at tryptophan codon of region 1 of the leader sequence. Hence, the regions 2 and 3 of the leader sequence base pair and prevents the formation of attenuator by not allowing the region 3 to pair with region 4.