The term 'transcriptional interference' (TI) is widely used but poorly defined in the literature. There are a variety of methods by which one can interfere with the process or the product of transcription but the term TI usually refers to the direct negative impact of one transcriptional activity on a second transcriptional activity in cis. Two recent studies, one examining Saccharomyces cerevisiae and the other Escherichia coli, clearly show TI at one promoter caused by the arrival of a transcribing complex initiating at a distant promoter. TI is potentially widespread throughout biology; therefore, it is timely to assess exactly its nature, significance and operative mechanisms. In this article, we will address the following questions: what is TI, how important and widespread is it, how does it work and where should we focus our future research efforts? What is transcriptional interference?In this article, we wish to define transcriptional interference (TI) specifically as the suppressive influence of one transcriptional process, directly and in cis on a second transcriptional process. Our definition of TI (see Glossary) excludes the kind of interference that results from the following: (i) the binding of a repressor to its operator overlapping a promoter [1]; (ii) promoter modification, such as methylation [2]; (iii) hindering the progress of an elongating RNA polymerase (RNAP) by DNA-bound obstacles (other than a second RNAP) [3]; (iv) the inactivation of RNAP by RNA regulators [4]; (v) the insulation of an enhancer site [5]; and (vi) RNA interference (RNAi) in which the product of one transcriptional unit interferes with the half-life of the product of a second transcriptional unit [6]. We exclude from our definition of TI examples whereby transcription interferes directly with a cellular activity rather than with transcription associated with cellular activity (e.g. the interference with chromosome replication in Saccharomyces cerevisiae as a result of transcription across its site of initiation [7]). We also exclude those cases of 'negative interference' whereby one transcriptional process, directly and in cis, enhances rather than suppresses a second transcriptional process, such as the fortuitous positioning of a gene within an active chromatin domain [8], chromatin remodelling that promotes intergenic transcription [9] and transcriptional coupling in which a promoter is activated by the activity of an upstream divergent promoter [10].TI is often asymmetric and results from the existence of two promoters, the strong (aggressive) promoter reducing the expression of the weak (sensitive) promoter (Figure 1). These promoters can be either: (i) convergent promoters directing converging transcripts that overlap for at least part of their sequence ( Figure 1a); (ii) tandem promoters, one upstream of the other but transcribing in the same direction, with their transcripts possibly but not necessarily overlapping ( Figure 1b); or (iii) overlapping promoters, either divergent, convergent or tandem, in whi...

Transcriptional interference with convergent transcription from face-to-face promoters is a potentially important form of gene regulation in all organisms. Using LacZ reporter studies, the mechanism of interference was determined for a pair of face-to-face prokaryotic promoters in which a strong promoter interferes 5.6-fold with a weak promoter, 62 bp away. The promoters were variously rearranged to test different models of interference. Terminating transcription from the strong promoter before it reached the weak promoter dramatically reduced interference, indicating a requirement for the passage of the converging RNAP over the weak promoter. Based on in vitro experiments showing a slow rate of escape for open complexes at the weak promoter and their sensitivity to head-on collisions with elongating RNAP, a "sitting duck" model of interference is proposed and supported with in vivo permanganate footprinting. The model is further supported by the analysis of a second set of prokaryotic face-to-face promoters.

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Magnesium-ion-mediated RNA-RNA loop-receptor interactions, in conjunction with gold nanoparticles derivatized with DNA, have been used to make self-assembled nanowires. A wire located between lithographically fabricated nanoelectrodes is demonstrated that exhibits activated conduction by electron hopping at temperatures in the 150-300 K range. These techniques have the ability to link particles between devices and in the future may be used to assemble practical circuits.