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Elsevier, Journal of Biological Chemistry, 45(290), p. 26954-26967, 2015

DOI: 10.1074/jbc.m115.679019

Elsevier, Journal of Biological Chemistry, 50(290), p. 29760, 2015

DOI: 10.1074/jbc.a115.679019

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Identification of the ISWI Chromatin Remodeling Complex of the Early Branching Eukaryote Trypanosoma brucei

Journal article published in 2015 by Tara M. Stanne, Stanne Tm, Narayanan Ms, Mani Shankar Narayanan, Sophie Ridewood, Alexandra Ling, Kathrin Witmer ORCID, Manish Kushwaha, Simone Wiesler, Bill Wickstead ORCID, Jennifer Wood, Gloria Rudenko ORCID
This paper is made freely available by the publisher.
This paper is made freely available by the publisher.

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Abstract

ISWI chromatin remodelers are highly conserved in eukaryotes and are important for the assembly and spacing of nucleosomes, thereby controlling transcription initiation and elongation. ISWI is typically associated with different subunits, forming specialised complexes with discrete functions. In the unicellular parasite Trypanosoma brucei which causes African sleeping sickness, TbISWI downregulates RNA polymerase I (Pol I) transcribed Variant Surface Glycoprotein (VSG) gene expression sites (ES) which are mono-allelically expressed. Here, we use tandem affinity purification to determine the interacting partners of TbISWI. We identify three proteins which do not show significant homology with known ISWI associated partners. Surprisingly, one of these is nucleoplasmin-like protein (NLP), which we had previously shown to play a role in ES control. In addition, we identify two novel ISWI partners: Regulator of Chromosome Condensation 1-like protein (RCCP) and phenylalanine/ tyrosine rich protein (FYRP), both containing protein motifs typically found on chromatin proteins. Knock-down of RCCP or FYRP in bloodstream form T. brucei results in derepression of silent VSG ESs, as had previously been shown for TbISWI and NLP. All four proteins are expressed and interact with each other in both major life-cycle stages, and show similar distributions at Pol I transcribed loci. They are also found at Pol II strand switch regions as determined with ChIP. ISWI, NLP, RCCP and FYRP therefore appear to form a single major ISWI complex in T. brucei (TbIC). This reduced complexity of ISWI regulation and the presence of novel ISWI partners highlights the early divergence of trypanosomes in evolution.