Human promoters are intrinsically directional

Area of Science:

• Molecular Biology
• Genetics
• Gene Regulation

Background:

• Eukaryotic promoters are often associated with divergent transcription, where reverse-oriented transcripts initiate upstream of annotated genes.
• This phenomenon has been proposed as a general characteristic of active promoters.

Purpose of the Study:

• To investigate the inherent directionality of the human basal RNA polymerase II transcriptional machinery.
• To determine the origin of reverse-oriented transcripts observed near eukaryotic promoters.

Main Methods:

• In vitro transcription assays were performed to analyze the transcriptional machinery.
• Nascent transcripts in HeLa cells were mapped to identify transcription start sites.
• DNase I accessibility assays were used to define proximal promoter boundaries.

Main Results:

• The human basal RNA polymerase II machinery and core promoters are inherently unidirectional.
• Reverse-oriented transcripts initiate from distinct, reverse-directed core promoters.
• Approximately half of all promoters are unidirectional, lacking upstream reverse core promoter elements.

Conclusions:

• Divergent transcription is not an intrinsic feature of the transcription process itself.
• The presence of both forward and reverse-directed core promoters explains the occurrence of divergent transcription.