title: USF1 recruits histone modification complexes and is critical for maintenance of a chromatin barrier.
abstract: The insulator element at the 5' end of the chicken beta-globin locus acts as a barrier, protecting transgenes against silencing effects of adjacent heterochromatin. We showed earlier that the transcription factor USF1 binds within the insulator and that this site is important for generating in adjacent nucleosomes histone modifications associated with active chromatin and, by inference, with barrier function. To understand the mechanism of USF1 action, we have characterized USF1-containing complexes. USF1 interacts directly with the histone H4R3-specific methyltransferase PRMT1. USF1, PRMT1, and the histone acetyltransferases (HATs) PCAF and SRC-1 form a complex with both H4R3 histone methyltransferase and HAT activities. Small interfering RNA downregulation of USF1 results in localized loss of H4R3 methylation, and other histone modifications associated with euchromatin, at the insulator. A dominant negative peptide that interferes with USF1 binding to DNA causes silencing of an insulated reporter construct, indicating abolition of barrier function. These results show that USF1 plays a direct role in maintaining the barrier, supporting a model in which the insulator works as a barrier by maintaining a local environment of active chromatin.
authors.affiliation: Laboratory of Molecular Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-0540, USA. sumingh@ufl.edu
authors.forename: Suming
authors.initials: S
authors.lastname: Huang
authors.forename: Xingguo
authors.initials: X
authors.lastname: Li
authors.forename: Timur M
authors.initials: TM
authors.lastname: Yusufzai
authors.forename: Yi
authors.initials: Y
authors.lastname: Qiu
authors.forename: Gary
authors.initials: G
authors.lastname: Felsenfeld
mesh_terms: D000818:Animals; D002460:Cell Line; D002645:Chickens; D002843:Chromatin / Q000737:chemistry / Q000378:metabolism*; D004912:Erythrocytes / Q000737:chemistry / Q000378:metabolism; D005786:Gene Expression Regulation; D020868:Gene Silencing; D006657:Histones / Q000737:chemistry / Q000378:metabolism*; D009690:Nucleic Acid Conformation; D011484:Protein-Arginine N-Methyltransferases / Q000235:genetics / Q000378:metabolism; D012319:RNA Polymerase II / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D051720:Upstream Stimulatory Factors / Q000235:genetics / Q000378:metabolism*; D050880:p300-CBP Transcription Factors / Q000235:genetics / Q000378:metabolism; D000099224:p300-CBP-Associated Factor
chemical_list: D002843:Chromatin; D006657:Histones; D011484:Protein-Arginine N-Methyltransferases; D012319:RNA Polymerase II; D034741:RNA, Small Interfering; D011993:Recombinant Fusion Proteins; D014157:Transcription Factors; D051720:Upstream Stimulatory Factors; D050880:p300-CBP Transcription Factors; D000099224:p300-CBP-Associated Factor