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ADP-ribosylation (ADPRylation) is a reversible posttranslational modification resulting in the covalent attachment of ADP-ribose (ADPR) moieties on substrate proteins. Naturally occurring protein motifs and domains, including WWEs, PBZs (PAR binding zinc fingers), and macrodomains, act as "readers" for protein-linked ADPR. Although recombinant, antibody-like ADPR detection reagents containing these readers have facilitated the detection of ADPR, they are limited in their ability to capture the dynamic nature of ADPRylation. Herein, we describe the preparation and use of poly(ADP-ribose) (PAR) Trackers (PAR-Ts)-optimized dimerization-dependent or split-protein reassembly PAR sensors containing a naturally occurring PAR binding domain fused to both halves of dimerization-dependent GFP (ddGFP) or split nano luciferase (NanoLuc), respectively. We also describe how these tools can be used for the detection and quantification of PAR levels in biochemical assays with extracts and in living cells. These protocols will allow users to explore the broad utility of PAR-Ts for detecting PAR in various experimental and biological systems., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Gene regulation in the nucleus requires precise control of the molecular processes that dictate how, when, and which genes are transcribed. The posttranslational modification (PTM) of histones in chromatin is an effective means to link cellular signaling to gene expression outcomes. The repertoire of histone PTMs includes phosphorylation, acetylation, methylation, ubiquitylation, and ADP-ribosylation (ADPRylation). ADPRylation is a reversible PTM that results in the covalent transfer of ADP-ribose units derived from NAD + to substrate proteins on glutamate, aspartate, serine, and other amino acids. Histones were the first substrate proteins identified for ADPRylation, over five decades ago. Since that time, histone ADPRylation has been shown to be a widespread and critical regulator of chromatin structure and function during transcription, DNA repair, and replication. Here, we describe a set of protocols that allow the user to investigate site-specific histone ADPRylation and its functional consequences in biochemical assays and in cells in a variety of biological systems. With the recent discovery that some cancer-causing histone mutations (i.e., oncohistone mutations) occur at functional sites of regulatory ADPRylation, these protocols may have additional utility in studies of oncology., (© 2023. The Author(s), under exclusive license to Springer Science+Business Media, LLC, part of Springer Nature.)

Nuclear poly(ADP-ribose) polymerases (PARPs), including PARPs 1, 2, and 3 and the Tankyrases, belong to a family of enzymes that can bind to chromatin and covalently modify histone- and chromatin-associated proteins with ADP-ribose derived from nuclear NAD + . The genomic loci where the nuclear PARPs bind and covalently modify chromatin are a fundamental question in PARP biology. Chromatin immunoprecipitation coupled with deep sequencing (ChIP-seq) has become an essential tool for determining specific sites of binding and modification genome-wide. Few methods are available, however, for localizing PARP-specific ADP-ribosylation events across the genome. Here we describe a variation of ChIP-seq, called Click-ChIP-seq, for identifying sites of ADP-ribosylation mediated by specific PARP family members. This method uses analog-sensitive PARP (asPARP) technology, including asPARP mutants and the alkyne-containing "clickable" NAD + analog 8-Bu(3-yne)T-NAD + . In this assay, nuclei from cells expressing an asPARP protein of interest are incubated with 8-Bu(3-yne)T-NAD + , which is incorporated into ADP-ribose modifications mediated only by that specific asPARP protein. The nuclei are then subjected to cross-linking with formaldehyde, and the protein-linked analog ADP-ribose is clicked to biotin using copper-catalyzed alkyne-azide "click" chemistry. The chromatin is fragmented, and the fragments containing analog ADP-ribose are enriched using streptavidin-mediated precipitation. Finally, the enriched DNA is analyzed by qPCR or deep-sequencing experiments to determine which genomic loci contain ADP-ribose modifications mediated by the specific PARP protein of interest. Click-ChIP-seq has proven to be a robust and reproducible method for identifying chromatin-associated, PARP-specific ADP-ribosylation events genome-wide.

ADP-ribosylation is a covalent posttranslational modification of proteins that is catalyzed by various types of ADP-ribosyltransferase (ART) enzymes, including members of the poly(ADP-ribose) polymerase (PARP) family. ADP-ribose (ADPR) modifications can occur as mono(ADP-ribosyl)ation, oligo(ADP-ribosyl)ation, or poly(ADP-ribosyl)ation, depending on the particular ART enzyme catalyzing the reaction, as well as the specific reaction conditions. Understanding the biology of ADP-ribosylation requires facile and robust means of generating and detecting the modification in all of its forms. Here we describe how to generate protein-linked mono(ADP-ribose), oligo(ADP-ribose), and poly(ADP-ribose) (MAR, OAR, and PAR, respectively) in vitro as an automodification of PARPs 1 or 3. First, epitope-tagged PARP-1 (a PARP polyenzyme) and PARP-3 (a PARP monoenzyme) are expressed individually in insect cells using baculovirus expression vectors, and purified using immunoaffinity chromatography. Second, the purified recombinant PARPs are incubated individually in the presence of different concentrations of NAD + (as a donor of ADPR groups) and sheared DNA (to activate their catalytic activities) resulting in various forms of auto-ADP-ribosylation. Third, the products are confirmed using ADPR detection reagents that can distinguish among MAR, OAR, and PAR. Finally, if desired, the OAR and PAR can be deproteinized. The protein-linked and free MAR, OAR, and PAR generated in these reactions can be used as standards, substrates, or binding partners in a variety of ADPR-related assays.

The PARP family of ADP-ribosyl transferases contains 17 members in human cells, most of which catalyze the transfer of the ADP-ribose moiety of NAD + onto their target proteins. This posttranslational modification plays important roles in cellular signaling, especially during cellular stresses, such as heat shock, inflammation, unfolded protein responses, and DNA damage. Knowing the specific proteins that are substrates for individual PARPs, as well as the specific amino acid residues in a given target protein that are ADP-ribosylated, is a key step in understanding the biology of individual PARPs. Recently, we developed a robust NAD + analog-sensitive approach for PARPs, which allows PARP-specific ADP-ribosylation of substrates that is suitable for subsequent copper-catalyzed azide-alkyne cycloaddition ("click chemistry") reactions. When coupled with proteomics and mass spectrometry, the analog-sensitive PARP approach can be used to identify the specific amino acids that are ADP-ribosylated by individual PARP proteins. In this chapter, we describe the key facets of the experimental design and application of the analog-sensitive PARP methodology to identify site-specific modification of PARP target proteins.

Transcriptional enhancers are DNA regulatory elements that are bound by transcription factors and act to positively regulate the expression of nearby or distally located target genes. Enhancers have many features that have been discovered using genomic analyses. Recent studies have shown that active enhancers recruit RNA polymerase II (Pol II) and are transcribed, producing enhancer RNAs (eRNAs). GRO-seq, a method for identifying the location and orientation of all actively transcribing RNA polymerases across the genome, is a powerful approach for monitoring nascent enhancer transcription. Furthermore, the unique pattern of enhancer transcription can be used to identify enhancers in the absence of any information about the underlying transcription factors. Here, we describe the computational approaches required to identify and analyze active enhancers using GRO-seq data, including data pre-processing, alignment, and transcript calling. In addition, we describe protocols and computational pipelines for mining GRO-seq data to identify active enhancers, as well as known transcription factor binding sites that are transcribed. Furthermore, we discuss approaches for integrating GRO-seq-based enhancer data with other genomic data, including target gene expression and function. Finally, we describe molecular biology assays that can be used to confirm and explore further the function of enhancers that have been identified using genomic assays. Together, these approaches should allow the user to identify and explore the features and biological functions of new cell type-specific enhancers.