The region of DNA which borders the 5' end of a transcription unit and where a variety of regulatory sequences are located.

Synonyms: Flanking Region, 5', 5' Flanking Sequence, Flanking Sequence, 5', 5' Flanking Regions, Flanking Sequences, 5', Regions, 5' Flanking, Sequences, 5' Flanking, Region, 5' Flanking, Sequence, 5' Flanking, Flanking Regions, 5', 5' Flanking Region, 5' Flanking Sequences