THE TOPOLOGY OF TRANSCRIPTION BY IMMOBILIZED POLYMERASES

Current models for RNA synthesis involve an RNA polymerase that tracks along a static template. However, research on chromatin loops suggest s that the template slides past a polymerase immobilized in a large tr anscription factory. The evidence for immobilized polymerases is revie wed, and a model for transcription by such fixed enzymes is presented. According to the model, gene activation would involve reducing gene-f actory distance and increasing the affinity of a promoter for a factor y. Locus controlling regions and enhancers would attach to a factory a nd increase the chances that a promoter could bind to a polymerase; af ter transcriptional termination, the gene would detach from the factor y. As some RNA processing occurs cotranscriptionally, processing sites are also likely to be associated with the factory. (C) 1996 Academic Press, Inc.