The region of DNA which borders the 3' end of a transcription unit and where a variety of regulatory sequences are located.

Synonyms: Region, 3' Flanking, Sequence, 3' Flanking, Flanking Region, 3', Flanking Sequences, 3', Flanking Sequence, 3', Flanking Regions, 3', Regions, 3' Flanking, 3' Flanking Sequences, Sequences, 3' Flanking, 3' Flanking Regions, 3' Flanking Region, 3' Flanking Sequence