Binding of HMG-I(Y) imparts architectural specificity to a positioned nucleosome on the promoter of the human interleukin-2 receptor alpha gene.
Transcriptional induction of the interleukin-2 receptor alpha-chain (IL-2Ralpha) gene is a key event regulating T-cell-mediated immunity in mammals. In vivo, the T-cell-restricted protein Elf-1 and the general architectural transcription factor HMG-I(Y) cooperate in transcriptional regulation of the human IL-2Ralpha gene by binding to a specific positive regulatory region (PRRII) in its proximal promoter. Employing chromatin reconstitution analyses, we demonstrate that the binding sites for both HMG-I(Y) and Elf-1 in the PRRII element are incorporated into a strongly positioned nucleosome in vitro. A variety of analytical techniques was used to determine that a stable core particle is positioned over most of the PRRII element and that this nucleosome exhibits only a limited amount of lateral translational mobility. Regardless of its translational setting, the in vitro position of the nucleosome is such that DNA recognition sequences for both HMG-I(Y) and Elf-1 are located on the surface of the core particle. Restriction nuclease accessibility analyses indicate that a similarly positioned nucleosome also exists on the PRRII element in unstimulated lymphocytes when the IL-2Ralpha gene is silent and suggest that this core particle is remodeled following transcriptional activation of the gene in vivo. In vitro experiments employing the chemical cleavage reagent 1,10-phenanthroline copper (II) covalently attached to its C-terminal end demonstrate that HMG-I(Y) protein binds to the positioned PRRII nucleosome in a direction-specific manner, thus imparting a distinct architectural configuration to the core particle. Together, these findings suggest a role for the HMG-I(Y) protein in assisting the remodeling of a critically positioned nucleosome on the PRRII promoter element during IL-2Ralpha transcriptional activation in lymphocytes in vivo.
Reeves
R
R
Biochemistry/Biophysics, School of Molecular Biosciences, Washington State University, Pullman 99164, USA. reevesr@mailwsu.edu
Leonard
W J
WJ
Nissen
M S
MS
D001483:Base Sequence; D001665:Binding Sites; D002843:Chromatin / Q000648:ultrastructure; D004268:DNA-Binding Proteins / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D025741:HMGA1a Protein; D006609:High Mobility Group Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D009707:Nucleosomes / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D011401:Promoter Regions, Genetic; D014176:Protein Biosynthesis; D015375:Receptors, Interleukin-2 / Q000235:genetics*; D012045:Regulatory Sequences, Nucleic Acid; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation
D002843:Chromatin; D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D009707:Nucleosomes; D015375:Receptors, Interleukin-2; D014157:Transcription Factors; D025741:HMGA1a Protein