ABSTRACT
The fidelity of transcription initiation is essential for accurate gene expression, but the determinants of start site selection are not fully understood. Rap1 and other General Regulatory Factors (GRFs) control the expression of many genes in yeast. We show that depletion of these factors induces widespread ectopic transcription initiation within promoters. This generates many novel non-coding RNAs and transcript isoforms with diverse stability, profoundly altering the coding potential of the transcriptome. Ectopic transcription initiation strongly correlates with altered nucleosome positioning. We show that Rap1 sterically constrains nucleosomes as its mere binding to the DNA can be sufficient for restoration normal nucleosome positioning, transcription initiation and gene expression. These results demonstrate an essential role for GRFs in the fidelity of transcription initiation and in the suppression of pervasive transcription, redefining current models of their function. They have general implications for the mechanism of transcription initiation and the control of gene expression.
HIGHLIGHTS
Rap1, Abf1 and Reb1 control the fidelity of transcription initiation and suppress pervasive transcription
Widespread ectopic transcription initiation in Rap1-deficient cells induces variegated alterations in gene expression
Altered nucleosome positioning in GRFs-defective cells correlate with ectopic transcription initiation.
Rap1 controls nucleosomes positioning and transcription initiation at least partially by a steric hindrance mechanism