RNA base sequence of the trp leader region

The four internally complementary sequences that participate in attenuation (yellow) are shown, as well as the two trp codons (red) in region 1 that act as a pause site for RNA polymerase.
The translational stop codon after region 1 may serve to prevent needless translation of those few full-length messages that are produced despite attenuation.
Attenuation is a regulatory mechanism in which ribosome positioning on an mRNA determines whether transcription of an operon will terminate before transcription of the structural genes begins.