RPB7 Antibody

What is RPB7 and what is its function in cells?

RPB7 (also known as POLR2G) is a core component of RNA polymerase II (Pol II), a DNA-dependent RNA polymerase responsible for synthesizing mRNA precursors and many functional non-coding RNAs. The full-length protein has a molecular weight of approximately 19,294 daltons and is primarily localized in the nucleus. RPB7 belongs to the Eukaryotic RPB7/RPC8 RNA polymerase subunit family .

From a functional perspective, RPB7 forms a subcomplex with RPB4 that binds to a pocket formed by RPB1, RPB2, and RPABC2 at the base of the polymerase clamp element. This subcomplex plays a critical role in locking the clamp in a closed conformation, which prevents double-stranded DNA from entering the active site cleft. Additionally, the RPB4-RPB7 subcomplex has the ability to bind single-stranded DNA and RNA .

What applications are RPB7 antibodies typically used for?

RPB7 antibodies are commonly employed in several experimental applications, with Western Blotting (WB) and ELISA being the most widely validated. Based on commercial antibody data, the following applications have been validated for RPB7 antibodies:

When selecting an RPB7 antibody, researchers should verify that the specific application they require has been validated for their target species .

How do I validate the specificity of an RPB7 antibody?

To ensure the specificity of an RPB7 antibody, implement the following validation steps:

• Western blot analysis: Run protein extracts from your experimental system alongside recombinant RPB7 protein (positive control). The antibody should detect a band at approximately 19 kDa corresponding to RPB7.

• Knockout/knockdown controls: If possible, use extracts from cells with RPB7 knockdown or knockout (if viable) as negative controls. Since RPB7 is essential for cell viability in many organisms, conditional knockdown systems may be necessary .

• Peptide competition assay: Pre-incubate the antibody with the immunizing peptide before probing your samples. This should abolish specific signals.

• Cross-reactivity assessment: Test the antibody against related proteins, particularly other RNA polymerase subunits, to ensure specificity.

• Immunoprecipitation followed by mass spectrometry: For confirming that the antibody truly captures RPB7 and its known binding partners like RPB4 .

What controls should I include in RPB7 co-immunoprecipitation experiments?

When performing co-immunoprecipitation (Co-IP) experiments with RPB7 antibodies, include the following controls:

• Input control: Reserve 5-10% of the pre-immunoprecipitation lysate to confirm protein expression levels.

• Negative antibody control: Use an isotype-matched irrelevant antibody (e.g., normal IgG from the same species as your RPB7 antibody).

• RPB4 detection: As RPB7 forms a stable complex with RPB4, detection of RPB4 in your immunoprecipitation confirms successful capture of the physiologically relevant RPB7 complex. In yeast studies, RPB7-HA tagging allows verification of both RPB7 immunoprecipitation and associated RPB4 levels .

• Reciprocal IP: Perform reverse Co-IP using antibodies against expected interactors (e.g., Rpb3 or TFIIB) to confirm the interaction from both perspectives .

• RPB7 mutant controls: If investigating specific domains, include RPB7 mutants (e.g., G149D) that disrupt certain interactions while maintaining others .

Research has demonstrated that when immunoprecipitating Rpb7-HA from yeast, Western blot analysis can detect co-immunoprecipitated Rpb3, TFIIB (Sua7), and Rpb4, confirming the association of these proteins in the RNA polymerase II complex .

How does RPB7 regulate transcription-coupled nucleotide excision repair (TCR)?

Recent research has revealed that RPB7 plays a crucial role in repressing transcription-coupled nucleotide excision repair (TCR). Studies using RPB7 mutants, particularly the G149D variant, have shown that:

• Repressive function: Wild-type RPB7 normally suppresses TCR in cells lacking Rad26 (a TCR factor). The repressive effect is particularly evident in rad7Δ rad26Δ yeast cells, which are highly UV-sensitive .

• Mutation effects: The RPB7 G149D mutation significantly increases UV resistance in rad7Δ rad26Δ cells by derepressing TCR. This mutation completely restores TCR in these cells but does not substantially affect TCR in rad7Δ cells where Rad26 is present .

• Molecular mechanism: RPB7 regulates TCR through interactions with the transcription elongation factor Spt5. The G149D mutation dramatically reduces the crosslinking between RPB7 (specifically at position H158) and Spt5, suggesting that altered RPB7-Spt5 interaction is a key mechanism in the derepression of TCR .

• Domain-specific effects: The oligonucleotide/oligosaccharide-binding (OB) domain of RPB7, particularly the surface containing G149, is critical for the repression of TCR. Mutations in this domain can derepress TCR without disrupting the essential functions of RPB7 in transcription .

Methodologically, researchers investigating RPB7's role in TCR should consider UV survival assays, site-directed mutagenesis of RPB7, and protein crosslinking studies to examine protein-protein interactions.

What structural domains of RPB7 are important for its interaction with other proteins?

RPB7 contains two main structural domains that mediate different protein interactions:

• RNA-binding domain (RNP):

  • Forms critical contacts with RPB4

  • Mutations in the N-terminal residues 2-5 (rpb7RNP-10) can cause cell lethality, indicating essential interactions

  • Contributes to the stability of the RPB4-RPB7 subcomplex

• Oligonucleotide/oligosaccharide-binding (OB) domain:

  • Contains key surfaces for interaction with Spt5

  • The G149 residue is particularly important for Spt5 interaction and TCR repression

  • Residues T111 and H113 also influence Spt5 interaction

  • The E100, E148, I151, and H158 positions can crosslink with Spt5

  • C-terminal deletion of residues 161-171 (rpb7OB-16) is lethal, indicating essential functions

Experimental approaches to study these domains include:

• Site-specific photo-crosslinking using the unnatural amino acid p-benzoyl-L-phenylalanine (Bpa) at specific positions

• Mutational analysis of surface residues

• Co-immunoprecipitation assays to detect altered protein interactions

• UV sensitivity assays in appropriate genetic backgrounds to assess functional consequences

Research has demonstrated that the Rpb7 OB surface (including G149) interacts with the KOW3 domain of Spt5, and mutations disrupting this interaction can derepress TCR .

How does the RPB4-RPB7 subcomplex contribute to RNA polymerase II function?

The RPB4-RPB7 subcomplex plays multiple crucial roles in RNA polymerase II (RNAPII) function:

• Structural stabilization: The subcomplex binds to a pocket formed by RPB1, RPB2, and RPABC2 at the base of the clamp element, locking it in the closed conformation. This prevents double-stranded DNA from inappropriately entering the active site cleft .

• Nucleic acid binding: The RPB4-RPB7 subcomplex binds single-stranded DNA and RNA, potentially facilitating transcript processing or stability .

• Transcription initiation complex integrity: Research using co-immunoprecipitation demonstrates that RPB4 is required for stable association of TFIIB with the RNAPII complex. When RPB4 is deleted (rpb4Δ), there is a significant reduction in TFIIB (Sua7) levels associated with RNAPII, even though similar levels of Rpb3 are immunoprecipitated .

• RPB7 stability: RPB4 is required for proper association of RPB7 with the RNAPII complex. In rpb4Δ cells, Rpb7-HA levels decrease, indicating that RPB4 contributes to RPB7 stability or incorporation into RNAPII .

• Termination complex formation: Evidence suggests that a complete 12-subunit RNAPII complex (including RPB4 and RPB7) is required for the stable association of TFIIB with a competitive RNAPII termination complex .

Researchers investigating the RPB4-RPB7 subcomplex should consider:

• Co-immunoprecipitation experiments to assess protein-protein interactions

• RPB4 deletion or mutation studies to evaluate effects on RPB7 and RNAPII function

• Crosslinking approaches to map interaction surfaces precisely

• In vitro reconstitution of RNAPII complexes with and without the RPB4-RPB7 subcomplex

What methods are most effective for studying RPB7-protein interactions?

Several complementary approaches are effective for investigating RPB7-protein interactions:

• Co-immunoprecipitation (Co-IP):

  • Particularly effective when using tagged versions of RPB7 (e.g., RPB7-HA)

  • Can detect interactions with other RNAPII subunits (e.g., RPB3) and transcription factors (e.g., TFIIB)

  • Comparison between wild-type and mutant cells (e.g., rpb4Δ) reveals dependency of interactions on specific factors

• Site-specific photo-crosslinking:

  • Incorporation of the unnatural amino acid p-benzoyl-L-phenylalanine (Bpa) at specific positions

  • Allows precise mapping of interaction surfaces

  • Demonstrated successful detection of RPB7-Spt5 interactions at specific residues (E100, E148, I151, H158, I160)

• Mutational analysis:

  • Random mutagenesis screening for functional phenotypes (e.g., UV sensitivity)

  • Targeted mutations of specific domains or residues

  • Functional analysis of mutants to correlate structural changes with phenotypic effects

• Yeast two-hybrid or mammalian two-hybrid assays:

  • Detection of direct binary interactions

  • Can be combined with deletion constructs to map interaction domains

• Pull-down assays with recombinant proteins:

  • In vitro verification of direct interactions

  • Can be used to test the effects of mutations or post-translational modifications

When designing RPB7 interaction studies, researchers should consider:

• The potential impact of epitope tags on protein function

• The need for controls to account for changes in protein stability

• The complementary nature of in vivo and in vitro approaches

• The possibility that some interactions may be transient or depend on specific cellular contexts

How should I optimize Western blotting protocols for RPB7 detection?

For optimal detection of RPB7 by Western blotting, consider the following methodological recommendations:

• Sample preparation:

  • Use nuclear extraction protocols to enrich for nuclear proteins

  • Include protease inhibitors to prevent degradation

  • Consider crosslinking approaches for preserving protein complexes if studying interactions

• Gel electrophoresis:

  • Use 12-15% polyacrylamide gels for optimal resolution of RPB7 (19.3 kDa)

  • Include positive controls (recombinant RPB7) and molecular weight markers

• Transfer conditions:

  • Optimize transfer time for small proteins (typically 60-90 minutes)

  • Consider semi-dry transfer systems for efficient transfer of smaller proteins

• Blocking and antibody incubation:

  • Test both BSA and milk-based blocking solutions (some epitopes are masked by milk proteins)

  • Optimize primary antibody dilution (typically 1:500 to 1:2000)

  • Consider overnight incubation at 4°C for improved sensitivity

• Detection method:

  • Enhanced chemiluminescence (ECL) is generally sufficient for RPB7 detection

  • Consider fluorescent secondary antibodies for quantitative analysis

Available commercial antibodies for RPB7 demonstrate reactivity with human, mouse, rat, and yeast samples, with Western blotting being the most commonly validated application .

How can I design effective co-immunoprecipitation experiments to study RPB7 complexes?

To design effective co-immunoprecipitation (Co-IP) experiments for studying RPB7 complexes:

• Antibody selection:

  • Choose antibodies raised against different epitopes for IP and detection

  • Consider using epitope-tagged RPB7 (e.g., RPB7-HA) for improved specificity and efficiency

  • Verify antibody specificity through Western blotting before proceeding with Co-IP

• Lysate preparation:

  • Use gentle lysis buffers to preserve protein complexes

  • Include phosphatase inhibitors to maintain post-translational modifications

  • Adjust salt concentration to maintain specific interactions while reducing background

• Experimental design:

  • Pull down RPB7 to detect interacting partners (e.g., RPB4, RPB3, TFIIB)

  • Perform reciprocal IPs to confirm interactions

  • Compare wild-type and mutant conditions to assess interaction requirements

• Controls:

  • Include IgG controls from the same species as your IP antibody

  • Reserve 5-10% of input lysate for comparison

  • When studying RPB7-RPB4 interactions, be aware that RPB7-HA levels decrease in rpb4Δ cells

  • When comparing wild-type and mutant conditions, adjust lysate amounts to equalize the immunoprecipitated protein

• Detection strategy:

  • Probe blots for known RPB7 interactors (RPB4, RPB3, TFIIB)

  • Consider mass spectrometry for unbiased identification of novel interactors

Research has demonstrated that when comparing Co-IP results between wild-type and rpb4Δ cells, adjusting the amount of whole cell extract to immunoprecipitate similar amounts of RPB7-HA allows for accurate assessment of the impact of RPB4 deletion on other interactions .

What genetic backgrounds are most informative for studying RPB7 function?

Several genetic backgrounds provide valuable insights into RPB7 function, particularly in yeast models:

• Repair-deficient backgrounds:

  • rad7Δ or rad16Δ: Deficient in global genomic repair (GGR)

  • rad26Δ: Deficient in transcription-coupled repair (TCR)

  • rad7Δ rad26Δ: Highly UV-sensitive due to deficiency in both repair pathways

• Transcription factor mutations:

  • spt4Δ: Deletion of transcription elongation factor Spt4

  • spt4Δ rad26Δ: Allows assessment of Spt4-independent repair mechanisms

• RPB7 mutations:

  • rpb7G149D: Derepresses TCR in the absence of Rad26

  • rpb7T111I-H113D: Affects interaction with Spt5

  • Various OB and RNP domain mutations to assess structural requirements

• Combined genetic backgrounds:

  • rpb7G149D rad7Δ rad26Δ: Tests RPB7 mutation effects in repair-deficient background

  • rpb7G149D rad7Δ rad26Δ spt4Δ: Assesses the interaction between RPB7 and Spt4-mediated functions

• Tagged protein strains:

  • RPB7-HA: Facilitates immunoprecipitation studies

  • Combinations of tagged strains with repair or transcription factor mutations

When designing studies with these genetic backgrounds, researchers should be aware that:

• Some RPB7 mutations are lethal due to its essential role in transcription

• The phenotypic effects of RPB7 mutations may vary across different genes

• UV sensitivity assays provide a functional readout for TCR activity

• Crosslinking studies in different genetic backgrounds can reveal the molecular basis of functional changes

Research has shown that the rpb7G149D mutation significantly increases UV resistance in rad7Δ rad26Δ cells but does not substantially affect UV resistance in rad7Δ cells, indicating a specific interaction with Rad26-dependent functions .

How do different RPB7 antibody types compare in research applications?

Different types of RPB7 antibodies offer varying advantages for specific research applications:

When selecting an RPB7 antibody, consider:

• Target species: Commercial antibodies show varying reactivity patterns, with options available for human, mouse, rat, yeast, and bacterial studies .

• Application requirements: While Western blot and ELISA applications are widely validated, some antibodies are also suitable for flow cytometry or specialized applications .

• Epitope location: Antibodies targeting different regions of RPB7 may yield different results, especially when studying protein interactions. Some commercial antibodies target the C-terminal region (aa 100-150), which may affect detection of certain complexes .

• Conjugation options: Some suppliers offer conjugated antibodies (biotin, FITC, HRP, Alexa Fluor) for specialized applications .

Research has successfully employed HA-tagged RPB7 for co-immunoprecipitation studies, demonstrating interactions with TFIIB, Rpb3, and Rpb4 in yeast systems .

How can RPB7 antibodies be used to study transcription mechanisms?

RPB7 antibodies serve as valuable tools for investigating various aspects of transcription mechanisms:

• Assembly of transcription initiation complexes:

  • Co-immunoprecipitation with RPB7 antibodies can detect associations with transcription factors like TFIIB

  • Comparison between wild-type and mutant cells reveals requirements for complex assembly

  • Studies have shown that a complete 12-subunit RNAPII complex is required for stable association with TFIIB

• Dynamics of RNAPII during elongation:

  • Chromatin immunoprecipitation (ChIP) using RPB7 antibodies can track RNAPII progression along genes

  • Comparison with other RNAPII subunit ChIPs provides insights into polymerase complex integrity

• Transcription-coupled repair processes:

  • RPB7 antibodies can be used to study how RNAPII interfaces with DNA repair machinery

  • Research has revealed RPB7's role in repressing transcription-coupled repair through interactions with Spt5

• Structural transitions in RNAPII:

  • RPB7, as part of the RPB4-RPB7 subcomplex, helps lock the clamp in closed conformation

  • Antibodies can be used to analyze how this subcomplex affects RNAPII structure and function

• Methodological approaches:

  • Western blotting: Detect RPB7 levels and modifications

  • Co-IP: Identify proteins that interact with RPB7

  • ChIP: Determine genomic locations of RPB7-containing complexes

  • ChIP-seq: Genome-wide profiling of RPB7 distribution

  • Proximity ligation assay: Visualize interactions in situ

When using RPB7 antibodies for transcription studies, researchers should consider:

• The essential nature of RPB7 means complete loss is lethal, requiring carefully designed mutational or conditional approaches

• RPB7 functions in concert with RPB4, so phenotypes may reflect disruption of the subcomplex rather than RPB7 alone

• Species-specific differences in RPB7 may affect antibody reactivity across experimental systems

What can we learn about DNA repair mechanisms using RPB7 antibodies?

RPB7 antibodies provide unique insights into DNA repair mechanisms, particularly transcription-coupled repair (TCR):

• RPB7's repressive role in TCR:

  • Recent research has revealed that RPB7 represses TCR through interactions with the transcription elongation factor Spt5

  • The RPB7 G149D mutation derepresses TCR in the absence of Rad26, demonstrating RPB7's regulatory function

• Experimental approaches using RPB7 antibodies:

  • UV survival assays in cells with wild-type vs. mutant RPB7 to assess repair capacity

  • DNA damage repair kinetics studies using ChIP with RPB7 antibodies

  • Co-immunoprecipitation to identify repair factors that interact with RNAPII through RPB7

  • Site-specific crosslinking to map interaction surfaces between RPB7 and repair factors

• Functional domains in DNA repair:

  • The RPB7 OB domain surface containing G149 interacts with Spt5's KOW3 domain

  • Mutations in this surface affect DNA repair without disrupting transcription

  • Different regions of RPB7 have distinct roles in regulating TCR versus other DNA damage response pathways

• Methodological considerations:

  • When studying repair mechanisms, genetic backgrounds deficient in either global genomic repair (rad7Δ or rad16Δ) or TCR (rad26Δ) allow for unambiguous assessment of repair pathway components

  • Combined mutations (rad7Δ rad26Δ) create systems highly sensitive to DNA damage, facilitating detection of rescue effects by RPB7 mutations

Research has demonstrated that specific RPB7 mutants (e.g., G149D) can completely restore TCR in rad7Δ rad26Δ cells but do not significantly affect TCR in rad7Δ cells where Rad26 is present, indicating a role in regulating Rad26-independent repair pathways .

How can researchers optimize RPB7 protein expression and purification for functional studies?

For optimal expression and purification of RPB7 for functional studies, researchers should consider:

• Expression system selection:

  • E. coli: Suitable for producing recombinant RPB7 alone, but may lack eukaryotic post-translational modifications

  • Yeast: Better for expressing functionally relevant RPB7, especially when co-expressed with RPB4

  • Insect cells: Good compromise between yield and eukaryotic modifications

• Expression strategies:

  • Co-expression with RPB4 enhances stability and solubility of RPB7

  • Affinity tags (His, GST, MBP) facilitate purification

  • Consider cleavable tags to remove after purification

  • Temperature optimization (often lower temperatures improve folding)

• Purification approaches:

  • Multi-step purification combining:

    • Affinity chromatography (based on tag)

    • Ion exchange chromatography

    • Size exclusion chromatography

  • When purifying the RPB4-RPB7 subcomplex, tag one subunit and rely on the strong interaction for co-purification

• Functional validation:

  • RNA binding assays to confirm activity

  • Interaction studies with known partners (e.g., other RNAPII subunits)

  • Structural analysis (circular dichroism, thermal shift assays) to confirm proper folding

• Considerations for mutant proteins:

  • Some mutations (e.g., G149D) maintain stability while altering specific functions

  • Other mutations may destabilize the protein, requiring optimization of expression conditions

  • Co-expression with binding partners may stabilize otherwise unstable mutants

When designing RPB7 expression constructs, researchers should note that:

• The N-terminal region (residues 2-5) and C-terminal region (residues 161-171) are essential for viability, and their mutation or deletion may affect protein stability and function

• RPB7's full functionality depends on proper interaction with RPB4, so isolated RPB7 may not reflect its physiological behavior

What novel research directions are emerging for RPB7 studies?

Several exciting research directions are emerging for RPB7 studies:

• Expanded roles in DNA damage response:

  • Recent discoveries show RPB7 represses transcription-coupled repair through interactions with Spt5

  • Evidence suggests RPB7 may have broader roles in DNA damage response beyond TCR

  • The OB domain appears to play positive roles in non-NER DNA damage repair and/or tolerance mechanisms

• Structural dynamics of transcription complexes:

  • RPB7, as part of the RPB4-RPB7 subcomplex, affects the conformational state of RNAPII by locking the clamp

  • Emerging research opportunities exist to investigate how this regulation impacts transcription fidelity and response to DNA damage

  • Cryo-EM and other structural techniques can reveal dynamic changes in these complexes

• Gene-specific effects of RPB7 mutations:

  • Studies show RPB7 mutations can enhance TCR in some genes but not others

  • Research into gene-specific effects of RPB7 could reveal regulatory mechanisms for gene expression

• RPB7 in disease contexts:

  • Potential connections to cancer biology through roles in transcription and DNA repair

  • Possible targets for therapeutic intervention in diseases associated with dysregulated transcription

• Methodological advances:

  • Site-specific crosslinking using unnatural amino acids has proven valuable for mapping RPB7 interactions

  • Combination with proteomics approaches can reveal the full interactome

  • Single-molecule techniques might reveal dynamic aspects of RPB7 function in real-time

• Post-translational modifications:

  • Investigation of how PTMs regulate RPB7 function in different cellular contexts

  • Potential cross-talk between transcription and repair pathways through RPB7 modifications

Researchers exploring these directions should consider:

• Combining genetic approaches (mutations, knockdowns) with biochemical and structural studies

• Leveraging advances in imaging and single-molecule techniques

• Using systems biology approaches to understand RPB7's role in the broader context of gene expression and genome maintenance

Recent studies revealing RPB7's novel function in TCR regulation suggest this RNAPII subunit has broader roles in DNA damage response beyond its known function in transcription, opening new avenues for investigation .

What are common challenges when working with RPB7 antibodies and how can they be addressed?

Researchers commonly encounter several challenges when working with RPB7 antibodies:

• Specificity issues:

  • Challenge: Cross-reactivity with other RNA polymerase subunits or proteins of similar size.

  • Solution: Validate antibody specificity using positive controls (recombinant RPB7) and negative controls (RPB7-depleted samples when possible). Consider using RPB7-tagged systems when native antibodies show poor specificity .

• Low signal strength:

  • Challenge: RPB7 is present at relatively low abundance compared to some other nuclear proteins.

  • Solution: Enrich for nuclear fractions; optimize extraction conditions; increase antibody concentration or incubation time; use signal enhancement systems like biotin-streptavidin amplification .

• Inconsistent immunoprecipitation:

  • Challenge: Variable efficiency in pulling down RPB7 complexes.

  • Solution: Test different antibodies targeting distinct epitopes; optimize buffer conditions (salt, detergent concentration); consider crosslinking approaches for transient interactions; use tagged RPB7 systems for more consistent results .

• Species cross-reactivity limitations:

  • Challenge: Antibodies validated for one species may not work in others.

  • Solution: Select antibodies raised against conserved epitopes for cross-species applications; validate each antibody in your specific model system; consider custom antibody development for uncommon model organisms .

• Background in immunofluorescence:

  • Challenge: High nuclear background when using RPB7 antibodies for imaging.

  • Solution: Increase blocking stringency; optimize antibody dilution; use monoclonal antibodies for higher specificity; include appropriate controls for secondary antibody binding.

When troubleshooting:

• Always run both positive and negative controls

• Consider the impact of fixation methods on epitope availability

• Test multiple antibody lots if inconsistent results are observed

• Remember that RPB7 function depends on its interaction with RPB4, so levels of RPB4 may affect RPB7 detection

How can I design effective controls for experiments using RPB7 antibodies?

Designing effective controls for RPB7 antibody experiments is critical for data interpretation:

• Western blotting controls:

  • Positive control: Recombinant RPB7 protein or extract from cells overexpressing RPB7

  • Loading control: Housekeeping protein (e.g., GAPDH, β-actin) or total protein stain (e.g., Ponceau S)

  • Specificity control: Peptide competition assay using the immunizing peptide

  • Size validation: Molecular weight markers to confirm the expected 19.3 kDa band

• Immunoprecipitation controls:

  • Input control: 5-10% of pre-IP lysate

  • Negative antibody control: Isotype-matched irrelevant antibody (e.g., normal IgG)

  • Reciprocal IP: Pull down with antibodies against known interactors (e.g., RPB4, RPB3)

  • Validation control: Detection of known RPB7 interactors in the IP fraction (e.g., RPB4)

• Genetic background controls:

  • Wild-type comparison: Always compare mutant strains to isogenic wild-type

  • Known phenotype validation: Include strains with established phenotypes (e.g., rad7Δ rad26Δ for UV sensitivity)

  • Complementation control: Rescue experiments with wild-type protein to confirm phenotypes are due to the intended mutation

• Sample preparation controls:

  • Nuclear/cytoplasmic fractionation validation: Confirm fraction purity using markers (e.g., histone H3 for nucleus, GAPDH for cytoplasm)

  • Protease inhibitor control: Samples with and without inhibitors to assess degradation

• Antibody validation controls:

  • Multiple antibodies: Use antibodies targeting different epitopes of RPB7

  • Tagged protein control: Compare detection of native vs. tagged RPB7 when possible

  • Knockdown validation: Reduced signal in samples with RPB7 knockdown (if viable)