Spt4 helps RNAPII pass the +2 nucleosome barrier in vivo

Aim and Methods: To understand the precise role of Spt4 in budding yeast, various high throughput sequencing techniques were used. Nucleosome positions were studied using MNase-seq in WT and spt4∆ cells. The position of RNAPII was examined using NET-seq in spt4∆ cells or cells in which Spt4 has been anchored away to the cytoplasm (Spt4 AA). RNAPII was also mapped in cells in which Spt5 has been anchored away to the cytoplasm (Spt5 AA). Steady-state transcript levels were assessed using RNA-seq in samples coupled with NET-seq. The position of the Spt4 on RNAPII was mapped at single nucleotide resolution using TEF-seq. With the same technique, the position of Spt5 on RNAPII was investigated in wild type (WT) and spt4 knock-out (spt4∆) cells. The position and levels of the pre-initiation complex were assessed using ChIP-seq on Sua7(TFIIB) in WT and spt4∆ cells. Results: The interaction between the Spt4/5 complex and RNAPII periodically changes as RNAPII transitions through nucleosomes. The dynamic interaction of Spt5 with RNAPII is dependent on Spt4. In spt4∆ and Spt4 AA cells, RNAPII distribution is altered in a similar way compared to their respective controls. After transcribing into nucleosomes, RNAPII accumulates upstream of nucleosome dyads, especially around the +2 nucleosome. In Spt5 AA cells, the distribution and amount of RNAPII on genes are severely affected. Nucleosome positions are altered in spt4∆ cells. Although the position of the +1 nucleosome remains unchanged, nucleosome spacing from this point is increased, and the level of increase in nucleosome spacing correlates with the level of RNAPII accumulation. Conclusion: This work suggests that Spt4 regulates nucleosome positioning by a mechanism related to transcription and promotes RNAPII movement through nucleosome barriers, especially the barrier set by the +2 nucleosome. MNase-seq in WT and spt4∆ in triplicates; Transcription elongation factor sequncing (TEF-seq) in WT and spt4∆ for Spt4 or Spt5; Native elongation transcript sequencing (NET-seq) in WT, spt4∆, Spt4-AA, and Spt5-AA; RNA-seq in WT, spt4∆, Spt4-AA, and Spt5-AA; ChIP-seq in WT and spt4∆ for Sua7.