Xrn1 influence on gene transcription results from the combination of general effects on elongating RNA pol II and gene-specific chromatin configuration [RNA-seq]

mRNA homeostasis is favored by crosstalk between transcription and degradation machineries. Both the Ccr4-Not and the Xrn1-decaysome complexes have been described to influence transcription. While Ccr4-Not has been shown to directly stimulate transcription elongation, the information available on how Xrn1 influences transcription is scarce and contradictory. In this study we have addressed this issue by mapping RNA polymerase II (RNA pol II) at high resolution, using CRAC and BioGRO-seq techniques in Saccharomyces cerevisiae. We found significant effects of Xrn1 perturbation on RNA pol II profiles across the genome. RNA pol II profiles at 5’ exhibited significant reductions in slope that were compatible with decreased elongation rates. This phenomenon was also observed soon after the nuclear pool of Xrn1 was depleted. Nucleosome mapping confirmed drastically altered chromatin dynamics. We also found an accumulation of arrested RNA pol II at the 3’ end, immediately upstream of polyadenylation sites of most genes, with particular incidence in those functionally related to regulatory processes. Lack of Xrn1 provoked alterations in RNA pol II CTD phosphorylation and increased recruitment of 3’ pre-mRNA processing factors. However, accumulation of RNA pol II at 3’ ends was rather related to the nucleosomal configuration of those regions. 2 RNA-seq samples: 1 wt and 1 mutant.