Assays for interaction of transcription factor with nucleosome

Assays for Acetylation and Other Acylations of Lysine Residues

Lysine acetylation refers to addition of an acetyl moiety to the epsilon-amino group of a lysine residue and is important for regulating protein functions in various organisms from bacteria to humans. This is a reversible and precisely controlled covalent modification that either serves as an on/off switch or participates in a codified manner with other post-translational modifications to regulate different cellular and developmental processes in normal and pathological states. This unit describes methods for in vitro and in vivo determination of lysine acetylation. Such methods can be easily extended for analysis of other acylations (such as propionylation, butyrylation, crotonylation, and succinylation) that are also present in histones and many other proteins. © 2017 by John Wiley & Sons, Inc.

Nucleosome dynamics: HMGB1 relaxes canonical nucleosome structure to facilitate estrogen receptor binding

High mobility group protein 1 (HMGB1) interacts with DNA and chromatin to influence the regulation of transcription, DNA repair and recombination. We show that HMGB1 alters the structure and stability of the canonical nucleosome (N) in a nonenzymatic, ATP-independent manner. Although estrogen receptor (ER) does not bind to its consensus estrogen response element within a nucleosome, HMGB1 restructures the nucleosome to facilitate strong ER binding. The isolated HMGB1-restructured nucleosomes (N′ and N″) remain stable and exhibit characteristics distinctly different from the canonical nucleosome. These findings complement previous studies that showed (i) HMGB1 stimulates in vivo transcriptional activation at estrogen response elements and (ii) knock down of HMGB1 expression by siRNA precipitously reduced transcriptional activation. The findings indicate that one aspect of the mechanism of HMGB1 action involves a restructuring of the nucleosome that appears to relax structural constraints within the nucleosome.

Autoimmunogenicity of the helix-loop-helix DNA-binding domain

Nonimmunogenic character of native DNA, and its high immunogenicity when presented in complex with the DNA-binding proteins indicate that the latter might contain molecular triggers of anti-DNA response. To find if this is the case, we have evaluated the autoimmunogenic potential of the main DNA-binding domain of HIV-1 reverse transcriptase that belongs to the canonical helix-loop-helix type. BALB/c mice were immunized with a peptide representing the domain, alone or in complex with the fragmented human DNA in the presence of an adjuvant. Mice were assessed for specific antibodies, autoantibodies against a panel of self-antigens; glomerular immunoglobulin deposition; and for the signs of autoimmune disease, such as proteinuria, and changes in the blood components. Immunization with the adjuvanted peptide-DNA complex induced autoantibodies against double-stranded DNA, histones, heterochromatin, and kidney proteins; glomerular IgG and IgA deposition; proteinuria; thrombocytopenia, and anemia. Altogether, this identifies the helix-loop-helix DNA-binding domain as one of the molecular triggers of autoimmunity to DNA and DNA-associated proteins. The experiments cast new light on the role of the DNA-binding retroviral proteins in the induction of autoimmunity, and on the origins of autoimmune complications in the microbial infections in general. It also implies that choosing the DNA-binding proteins as vaccine candidates should be done with precaution.

Analysis of protein lysine acetylation in vitro and in vivo

Protein lysine acetylation, referring to acetylation of the epsilon-amino group of a lysine residue, has recently emerged as an important post-translational modification for regulating protein functions in various organisms. Like phosphorylation, lysine acetylation is a rapidly reversible and precisely controlled covalent modification that serves as a simple on/off switch or participates in a codified manner with other post-translational modifications to regulate protein functions in different cellular and developmental processes. This unit describes and discusses methods used for in vitro and in vivo determination of lysine acetylation.

Multiple nucleosome positioning sites regulate the CTCF-mediated insulator function of the H19 imprinting control region

The 5' region of the H19 gene harbors a methylation-sensitive chromatin insulator within an imprinting control region (ICR). Insertional mutagenesis in combination with episomal assays identified nucleosome positioning sequences (NPSs) that set the stage for the remarkably precise distribution of the four target sites for the chromatin insulator protein CTCF to nucleosome linker sequences in the H19 ICR. Changing positions of the NPSs resulted in loss of both CTCF target site occupancy and insulator function, suggesting that the NPSs optimize the fidelity of the insulator function. We propose that the NPSs ensure the fidelity of the repressed status of the maternal Igf2 allele during development by constitutively maintaining availability of the CTCF target sites.