Negative regulation of trp operon occurs by
Negative regulation of trp operon occurs through dual overlapping mechanisms where repressor binding directly reduces promoter activity. Active holorepressor TrpR-tryptophan complex occupies operator site overlapping transcription start site, forming high-affinity nucleoprotein complex that sterically impedes RNA polymerase holoenzyme binding and interferes with isomerization from closed to open complex. This specific interference reduces initiation frequency approximately seventyfold. Second attenuation layer further lowers productive elongation tenfold via premature termination at leader seq
Ref: Wikipedia trp operon – negative regulation by repressor blocking RNA polymerase, plus attenuation secondary control.