Intron DNA sequences can be more important than the proximal promoter in determining the site of transcript initiation

The site at which transcription begins is traditionally thought to be determined in the proximal promoter by assembly of the pre-initiation complex just upstream of the transcription start site (TSS). New results from Gallegos and Rose challenge this assumption. Prior studies have shown that the presence of an intron near the TSS can boost transcript levels, an effect known as intron-mediated enhancement (IME). While exploring the constraints of intron position on IME, the authors found that in some conditions introns can change the location of the TSS and substitute for a missing proximal promoter. The mechanism of these effects is not clear, but the authors specture it may involve the formation of a region of open DNA that enables access by the transcriptional machinery. Plant Cell ​10.​1105/​tpc.​17.​00020