The LRS and SIN domains: two structurally equivalent but functionally distinct nucleosomal surfaces required for transcriptional silencing.
Genetic experiments have identified two structurally similar nucleosomal domains, SIN and LRS, required for transcriptional repression at genes regulated by the SWI/SNF chromatin remodeling complex or for heterochromatic gene silencing, respectively. Each of these domains consists of histone H3 and H4 L1 and L2 loops that form a DNA-binding surface at either superhelical location (SHL) +/-2.5 (LRS) or SHL +/-0.5 (SIN). Here we show that alterations in the LRS domain do not result in Sin(-) phenotypes, nor does disruption of the SIN domain lead to loss of ribosomal DNA heterochromatic gene silencing (Lrs(-) phenotype). Furthermore, whereas disruption of the SIN domain eliminates intramolecular folding of nucleosomal arrays in vitro, alterations in the LRS domain have no effect on chromatin folding in vitro. In contrast to these dissimilarities, we find that the SIN and LRS domains are both required for recruitment of Sir2p and Sir4p to telomeric and silent mating type loci, suggesting that both surfaces can contribute to heterochromatin formation. Our study shows that structurally similar nucleosomal surfaces provide distinct functionalities in vivo and in vitro.
Fry
Christopher J
CJ
Program in Molecular Medicine, University of Massachusetts Medical School, Biotech 2, Suite 210, Worcester, MA 01605, USA.
Norris
Anne
A
Cosgrove
Michael
M
Boeke
Jef D
JD
Peterson
Craig L
CL
D000483:Alleles; D000818:Animals; D002843:Chromatin / Q000737:chemistry / Q000235:genetics; D004271:DNA, Fungal / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D020868:Gene Silencing; D006657:Histones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D009707:Nucleosomes / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic; D029867:Xenopus Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D014982:Xenopus laevis
D002843:Chromatin; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D006657:Histones; D009707:Nucleosomes; D011994:Recombinant Proteins; D029867:Xenopus Proteins