Taken together, we predict that the dispersed Sir3 in htb-T122E cells may be due to compromised SIR binding to telomere. The results presented here show that an appropriately arrayed chromatin mediated by H2B C-terminus is required for optimal SIR binding and the subsequent formation of telomeric chromatin in yeast, which leads to gene silencing. It has been proposed that the BAH domain of Sir3 binds at the gap between nucleosomes in the 11 nm chromatin fiber, where the aC helix of H2B facilitates the establishment of internucleosomal contacts. Although the nucleosome has long been assumed to fold into 30 nm chromatin fiber, accumulative results from cryoelectron microscopy have not detected 30 nm chromatin fibers in interphase nuclei. This view is supported by a recent paper by Danesh Moazed��s laboratory. Moazed and colleagues used a purified system to reconstruct SIR mediated heterochromatin in vitro. They observe the formation of extended SIR-nucleosome filaments mediated by the conserved BAH domain in Sir3, indicating that the association of the SIR complex with nucleosome arrays may occur without further chromatin compaction into a 30 nm fiber. Our results suggest that T122 of the H2B C-terminus may be required for its ability to maintain an orderly nucleosome array through inter-nucleosomal contacts. Therefore, our result supports a model that the SIR complex binds to and spreads along a regularly aligned chromatin fiber that requires the H2B C-terminus. We have shown that the residue T122 is LY2109761 critical for silencing and appropriate chromatin structure specifically at the telomere, but it remains unclear as to how the T122E substitution impacts on chromatin structure and accessibility. The crystal structure of yeast nucleosome suggests that H2B T122 faces towards the surface of the nucleosome disk, which may contribute to the unique feature of this residue. Through our sucrose gradient sedimentation assay, we show that H2Bub1 and Sir4 are most likely not involved in increasing the mobility of telomeric heterochromatin of htb1-T122E. As such, we suggest that perhaps the faster sedimentation of Selumetinib clinical trial htb1-T122E chromatin is induced by altered inter-nucleosomal interactions, resulting in disarrayed and clumped nucleosomes within heterochromatin, causing aberrant compaction. Confirmation of this hypothesis will necessitate visualization of the chromatin of the mutant strain by electron microscopy, and the modeling of inter-nucleosomal interactions, to determine which residues of H3 interact with H2B C-terminus. However, we cannot completely rule out the possibility that a disruption of the levels of H2Bub1 affects telomeric chromatin compaction. The ubiquitylation of H2B is dynamic in nature, and these fluctuations may be essential for telomeric chromatin structure, which itself is also flexible and permissive.