Brophy and Voigt report characterizing antisense promoters to tune the transcription and translation of a forward-facing gene, and to build a simple NOT circuit. They note that the effects of antisense promoters on repressing gene expression is largely context-independent, and that level of repression correlates well with the strength of the antisense promoter. According to their model, two mechanisms contribute equally to this phenomenon. Most obviously, antisense promoters create antisense RNA which base pair with mRNA to obstruct translation. Collisions between RNA polymerases heading opposite directions on the same gene also contribute. Their work can be found here.