TRANSCRIPTIONAL INTERFERENCE PERTURBS THE BINDING OF SP1 TO THE HIV-1PROMOTER

Transcriptional interference between adjacent genes has been demonstra ted in a variety of biological systems, To study this process in RNA p olymerase II (pol II) transcribed genes we have analysed the effect of transcription on tandem HIV-1 promoters integrated into the genome of HeLa cells, We show that transcriptional activation at the upstream p romoter reduces transcription from the downstream promoter, as compare d with basal transcription conditions (in the absence of an activator) , Furthermore, insertion of a strong transcriptional termination eleme nt between the two promoters alleviates this transcriptional interfere nce, resulting in elevated levels of transcription from the downstream promoter, Actual protein interactions with the downstream (occluded) promoter were analysed by in vivo footprinting, Binding of Sp1 transcr iption factors to the occluded promoter was reduced, when compared wit h the footprint pattern of the promoter protected by the terminator, T his suggests that promoter occlusion is due to disruption of certain t ranscription factors and that it can be blocked by an intervening tran scriptional terminator, Chromatin mapping with DNase I indicates that a factor binds to the termination element under both basal and induced conditions.