Figure 8.

A model for a silenced superstructure at HMR. The E and the I silencers interact to form a loop, creating distinct boundaries for Sir protein association. Nucleosomes are tightly packed throughout the loci, with a secondary loop burying the promoter in the chromatin superstructure, excluding access by RNA polymerase in vivo and antibodies in cross-linked chromatin in vitro. Sir proteins associate with the nucleosomes throughout the locus and are also buried within the conformation at the promoter region. The tRNA gene associates with the silenced superstructure and interacts with the Sir complex mediated by Sir2 cohesin binding.