Practice question

Transcription unit represents functional extent of DNA copied into single primary RNA by polymerase moving from initiation to termination signals. Boundaries include promoter upstream where holoenzyme binds sigma factor and recognizes consensus elements, transcription start site, 5' untranslated sequence, coding region or polycistronic cistrons in bacteria, 3' untranslated region, and terminator sequence triggering release. In eukaryotes unit also includes introns later spliced. Unit distinguishes replicon which drives replication initiation and operon conceptual organization. Understanding unit architecture clarifies linkage between regulatory inputs controlling RNA output and processing events.