Spt6-Spn1 interaction is required for RNA Polymerase II association and precise nucleosome positioning along transcribed genes

Spt6-Spn1 is an essential histone chaperone complex that associates with RNA Polymerase II (RNAPII) and reassembles nucleosomes during gene transcription. While Spt6-Spn1 interaction is important to its histone deposition and transcription functions, a precise understanding of how Spt6-Spn1 association contributes to its functions is still limited. Here, using temperature sensitive alleles of spt6 and spn1 that disrupt their interaction, we show that Spt6-Spn1 association is broadly important for its interaction with the elongating RNAPII complex and nucleosomes. Using micrococcal nuclease (MNase)-based chromatin occupancy profiling, we further find that Spt6-Spn1 interaction is required for maintaining the preferred nucleosome positioning generated from replication-dependent histone deposition at actively transcribed genes. These analyses also reveal an overall shift of nucleosomes towards the 5’ end of genes that correlates with decreased RNAPII levels. While loss of Spt6 and Spn1 function is known to promote cryptic transcription, the nucleosome defects found in spt6 and spn1 mutants that interfere with their interaction were observed broadly across transcribed genes, further highlighting the role of DNA sequence as a mediator of cryptic transcription when nucleosomes positioning is altered. Taken together, these findings reveal Spt6-Spn1 interaction is key to its association with elongating RNAPII and for its ability to precisely organize nucleosomes across transcription units. RNA-seq at 30° and 37° C, MNase-seq at 37° C, and RNA PolII ChIP-seq at 37° C in yeast, across wild-type (S288C), spt6-F249K, spn1-R263D, and spn1-F267E mutant strains.