Figure 5.

Schematic model of rSir3p-dependent cross-linking of chromatin fibers into defined supramolecular structures. Shown is a portion of two nucleosomal arrays bridged together through interactions of rSir3p with the core histone H3 and/or H4 tail domains. Sir3p is drawn as an oligomer for the purposes of illustration only. H3 and H4 tail domains of each nucleosome are indicated by straight lines. Arrows indicate the positions of the EcoRI sites. Such a mechanism is proposed to facilitate both the formation of specific, transcriptionally silent higher order chromosomal domains associated with heterochromatin and telomeric clustering in vivo (see text).