The phenomenon that occurs in the trp operon which involves such alterations is Attenuation. Trp operon is a group of genes that are used or transcribed together and codes for the components for the production of tryptophan. This phenomenon of attenuation is a mechanism for reducing expression of the trp operon when levels of tryptophan are high. However, rather than blocking initiation of transcription, attenuation prevents completion of transcription.