Proteomic profiling of yeast heterochromatin connects direct physical and genetic interactions

Abstract

Heterochromatin domains are stably-repressed chromatin structures composed of a core assembly of silencing proteins that condense adjacent nucleosomes. The minimal heterochromatin structure can serve as a platform for recruitment of complementary regulatory factors. We find that a reconstituted budding yeast heterochromatin domain can act as a platform to recruit multiple factors that play a role in regulating heterochromatin function. We uncover the direct interaction between the SIR heterochromatin complex and a chromosomal boundary protein that restricts the spread of heterochromatin. We find that the SIR complex relieves a mechanism of auto-inhibition within the boundary protein Yta7, allowing the Yta7 bromodomain to engage chromatin. Our results suggest that budding yeast shares with other eukaryotes the ability to establish complex heterochromatin domains that coordinate multiple mechanisms of silencing regulation through physical interactions.

The ATAD2/ANCCA homolog Yta7 cooperates with Scm3 HJURP to deposit Cse4 CENP-A at the centromere in yeast

“…Yta7 furthermore has been described as a boundary factor that prevents the spreading of SIR heterochromatin across the tRNA boundary that lies next to the silent HMR locus (24,30). Accordingly, Yta7 binds in vitro to reconstituted yeast heterochromatin, and it interacts in vivo with SIR heterochromatin (31). Yta7 purified from yeast is associated with all four core histones as well as with the histone variant H2A.Z (24,28).…”

Mass Spectrometry to Study Chromatin Compaction

“…This approach was recently revamped by Iglesias and colleagues [109], who used the HP1 yeast homolog Swi6 to enrich heterochromatic domains in Schizosaccharomyces pombe. Similarly, Zukowski and colleagues assembled a repressive heterochromatin domain from purified components, conjugated to magnetic beads, to recruit factors that play a role in regulating heterochromatin function [110].…”