Gene loops juxtapose promoters and terminators in yeast.

Mechanistic analysis of transcriptional initiation and termination by RNA polymerase II (PolII) indicates that some factors are common to both processes. Here we show that two long genes of Saccharomyces cerevisiae, FMP27 and SEN1, exist in a looped conformation, effectively bringing together their promoter and terminator regions. We also show that PolII is located at both ends of FMP27 when this gene is transcribed from a GAL1 promoter under induced and noninduced conditions. Under these conditions, the C-terminal domain of the large subunit of PolII is phosphorylated at Ser5. Notably, inactivation of Kin28p causes a loss of both Ser5 phosphorylation and the loop conformation. These data suggest that gene loops are involved in the early stages of transcriptional activation. They also predict a previously unknown structural dimension to gene regulation, in which both ends of the transcription unit are defined before and during the transcription cycle.