Silent chromatin in yeast: an orchestrated medley featuring Sir3p

Abstract

Extensive regions of chromosomes can be transcriptionally repressed through silencing mechanisms mediated by complex chromatin structures. One of the most refined molecular portraits of silenced chromatin comes from studies of the silent mating‐type loci and telomeres of S. cerevisiae. In this budding yeast, the Sir3p silent information regulator emerges as a critically important silencing component that interacts with nucleosomes and other silencing proteins. Not only is it essential for silencing, but Sir3p is also capable of spreading silenced chromatin when its dosage is increased. Sir3p is a target of mitogen‐activated protein (MAP) kinase cascade regulation and has significant similarity to the Orc1p subunit of the DNA replication origin recognition complex. Thus, in concert with other silencing proteins, Sir3p appears poised to respond to cellular signals and reprogram silencing through replication‐associated assembly of repressive chromatin structures. BioEssays 20:30–40, 1998. © 1998 John Wiley & Sons, Inc.

Rheostat Control of Gene Expression by Metabolites

“…If SIR proteins can spread along chromatin, then what stops the complex from entering genomic regions that need to stay active? Clearly, overall SIR protein concentrations determine how far silencing spreads (Stone and Pillus, 1998). In addition, the HAT Sas2 and the acetylhistone binding Bdf1 bromodomains buffer euchromatin and maintain it transcriptionally active through H4 Lys16 acetylation (Kimura et al, 2002;Ladurner et al, 2003;Suka et al, 2002).…”

Role of Histone Acetylation in the Assembly and Modulation of Chromatin Structures

“…As a complement to these findings, histone colleagues (168) showed that in duck erythroblasts nascent H4 was found in un-, mono-, and dimodified deacetylation has been mechanistically tied to gene repression, as evidenced by transcriptional silencing isoforms, the latter described as a simultaneously monoacetylated/monophosphorylated species. It was in yeast (24,188), and by the recruitment of histone deacetylase (HDAC) by factors such as the repressor also observed that 20 min after chromatin assembly, at least 50% of the new H4 was present in the un-Rb (26, 128,131) and the methyl-CpG-binding protein MeCP2 (96,146,221). The involvement of dynamic modified form, demonstrating acetate and/or phosphate turnover.…”

Duplication and Maintenance of Heterochromatin Domains

“…The existence of local concentrations of specific proteins has been proposed to compartmentalize chromatin regions, creating an index system for the nucleus (Gasser and Laemmli, 1987;Stone and Pillus, 1998). The local concentration of specific proteins, such as Hp1␣ and -␤, could also be critical for defining domains that should be repressed.…”