Genome-wide association of Sus1 with RNAPII and tRNA genes depends on the distinctive SAGA subunits Spt8 and Spt7

We have analyzed the global effect of the conserved transcription-mRNA export factor Sus1 on transcription and its association with chromatin. We used genomic run-on experiments to show that Sus has a broad impact on the stability of most RNA polymerase II-transcribed genes. Genome association of Sus1 by the chromatin immunoprecipitation technique showed that Sus1 was widely distributed throughout coding regions, tending to accumulate towards the 3’ ends of highly transcribed transcription factor IID (TFIID) and Spt-Ada-Gcn5 acetyltransferase (SAGA) dependent genes. This accumulation depends on growth conditions, the transcriptional rate and whether the genes are TFIID- or SAGA-regulated. Validation of Sus1 occupancy data also revealed that Sus1 appears at tRNAs. Concomitantly, deletion of SUS1 leads to tRNA overexpression. In addition, we discovered that distinctive SAGA subunits Spt8 and Spt7 play a key role in Sus1 enrichment at the 3’ ends of SAGA-regulated genes upon temperature shift and at tRNAs. Thus, our study identifies the molecular mechanisms by which a SAGA factor is recruited genome-wide, and provides evidence of a more general role for this conserved coactivator in eukaryotic transcription. 12 samples, 4 strains (WT, spt8Δ, spt7-1180, spt8Δspt7-1180), 3 replicates per strain