RAD9 Antibody

What is RAD9 and what are its primary cellular functions?

RAD9 (RAD9A) is a component of the 9-1-1 cell-cycle checkpoint response complex (along with RAD1 and HUS1) that plays major roles in DNA repair and cell cycle regulation . The protein is recruited to DNA lesions upon damage by the RAD17-replication factor C (RFC) clamp loader complex . It functions as a sliding clamp platform on DNA for several proteins involved in long-patch base excision repair (LP-BER) . Additionally, RAD9 possesses 3'→5' double-stranded DNA exonuclease activity . Research has demonstrated RAD9's involvement in multiple DNA repair pathways including homologous recombination repair, base-pair excision repair, and DNA mismatch repair . RAD9 also plays critical roles in telomere stability and can interact with proteins like MLH1 and RAD51 .

What types of RAD9 antibodies are available for research applications?

Several RAD9 antibodies are available for research, including rabbit polyclonal antibodies that are suitable for various applications. For instance, ab70810 from Abcam is a rabbit polyclonal antibody suitable for immunohistochemistry-paraffin (IHC-P), immunoprecipitation (IP), and western blotting (WB) . Another example is DF6678 from Affinity Biosciences, which is also a rabbit polyclonal antibody validated for WB and IHC applications and shows reactivity with human, mouse, and rat samples . These antibodies are typically raised against synthetic peptides within the human RAD9A sequence .

How is RAD9 protein structurally organized and what are its key domains?

RAD9 is a 42-43 kDa protein containing multiple functional domains . The protein sequence (UniProt Q99638) contains regions essential for its interactions with other proteins in the DNA damage response pathways . RAD9 undergoes alternative hyperphosphorylation and can exist in multiple forms in unperturbed cells . The C-terminal region of RAD9 is particularly important for its interactions with checkpoint proteins, while specific residues like S160 are crucial for interaction with repair proteins such as MLH1 . The protein contains sites for various post-translational modifications that regulate its activity and interactions with other proteins .

What are the optimal conditions for using RAD9 antibodies in Western blotting?

For Western blotting with RAD9 antibodies, researchers should consider the following protocol elements:

• Sample preparation: Nuclear extracts are often preferred as RAD9 is primarily a nuclear protein .

• Protein denaturation: Standard denaturation in SDS-loading buffer is appropriate.

• Expected molecular weight: Look for bands at approximately 42-43 kDa .

• Blocking: 5% non-fat milk or BSA in TBST is typically effective.

• Antibody dilution: Follow manufacturer recommendations (typically 1:1000 to 1:2000) .

• Detection method: Both chemiluminescence and fluorescence-based detection are suitable.

Note that RAD9 can exist in multiple phosphorylated forms, potentially resulting in several bands or a ladder-like appearance on Western blots .

How can I optimize immunoprecipitation protocols with RAD9 antibodies?

For effective immunoprecipitation of RAD9 and its interacting partners:

• Cell lysis: Use a buffer containing 50 mM Tris-HCl (pH 7.5), 150 mM NaCl, 1% NP-40 or Triton X-100, with protease and phosphatase inhibitors.

• Pre-clearing: Pre-clear lysates with protein A/G beads to reduce background.

• Antibody binding: Incubate lysates with RAD9 antibody (2-5 μg) overnight at 4°C .

• Bead capture: Add protein A/G beads and incubate for 1-2 hours at 4°C.

• Washing: Perform at least 4-5 washes with lysis buffer.

• Elution: Use either gentle elution with peptide competition or direct boiling in SDS sample buffer.

When studying RAD9 interactions, such as with MLH1, this protocol has successfully demonstrated physical interactions between these proteins .

What controls should be included when using RAD9 antibodies in immunohistochemistry?

When performing immunohistochemistry with RAD9 antibodies, include these essential controls:

• Positive control: Use tissues or cells known to express RAD9, such as proliferating B cells or cell lines with confirmed RAD9 expression .

• Negative control: Include serial sections with either no primary antibody or isotype-matched non-specific IgG.

• Peptide competition: Pre-incubate the antibody with the immunizing peptide to verify specificity.

• siRNA validation: When possible, include samples where RAD9 expression has been knocked down via siRNA .

• Comparison with other RAD9 antibodies: If available, confirm staining patterns with a different RAD9 antibody.

For paraffin-embedded tissues, antigen retrieval (typically heat-induced in citrate buffer pH 6.0) is crucial for optimal staining .

How can RAD9 antibodies be used to study the 9-1-1 complex formation and function?

To investigate the 9-1-1 complex (RAD9-RAD1-HUS1):

• Co-immunoprecipitation: Use RAD9 antibodies to pull down the complex, followed by Western blotting for RAD1 and HUS1 .

• Chromatin immunoprecipitation (ChIP): Apply RAD9 antibodies in ChIP assays to identify genomic binding sites of the 9-1-1 complex at DNA damage sites .

• Immunofluorescence co-localization: Perform double immunofluorescence with antibodies against RAD9 and other 9-1-1 components to visualize complex formation at DNA damage foci .

• Proximity ligation assay (PLA): Use RAD9 antibody in combination with antibodies against other complex components to directly visualize protein-protein interactions in situ.

• FRET analysis: Combine with fluorescently tagged components to study complex dynamics.

Research has shown that the 9-1-1 complex is recruited to DNA lesions and stimulates DNA polymerase beta activity by increasing its affinity for damaged DNA .

What approaches can be used to study RAD9's role in different DNA repair pathways?

To investigate RAD9's roles in multiple repair pathways:

• DNA mismatch repair (MMR):

  • Use in vitro MMR assays with extracts from cells where RAD9 has been depleted or mutated

  • Study RAD9-MLH1 interactions through co-IP and functional assays

  • Analyze microsatellite instability in RAD9-deficient cells

• Base excision repair (BER):

  • Measure BER activity using synthetic DNA substrates in extracts with/without RAD9

  • Analyze RAD9 recruitment to BER sites via ChIP or immunofluorescence

  • Study interactions with BER proteins like POLB, FEN1, and LIG1

• Homologous recombination repair (HRR):

  • Analyze RAD51 focus formation in RAD9-deficient cells

  • Perform DR-GFP reporter assays to measure HRR efficiency

  • Study RAD9-RAD51 interactions through co-IP experiments

• Telomere stability:

  • Analyze telomere associations and losses in metaphase spreads from RAD9-depleted cells

  • Measure telomere length using Q-FISH or Southern blotting

  • Perform ChIP to detect RAD9 at telomeres

Research has shown that disruption of RAD9-MLH1 interaction (e.g., through the S160A mutation) specifically reduces MMR activity without affecting other RAD9 functions .

How can we assess the impact of RAD9 phosphorylation on its function using antibodies?

RAD9 undergoes multiple phosphorylation events that regulate its functions:

• Phospho-specific antibodies: Where available, use antibodies recognizing specific phosphorylated residues of RAD9.

• Phos-tag SDS-PAGE: Combine with RAD9 antibodies to separate and detect different phosphorylated forms.

• Lambda phosphatase treatment: Compare RAD9 mobility before and after phosphatase treatment to identify phosphorylated forms.

• Immunoprecipitation followed by mass spectrometry:

  • Immunoprecipitate RAD9 using validated antibodies

  • Submit samples for phosphopeptide analysis by mass spectrometry

  • Quantify changes in phosphorylation patterns after DNA damage

• Site-directed mutagenesis combined with functional assays:

  • Create phospho-mimetic or phospho-dead mutants

  • Assess their functional impact using repair assays

  • Compare immunoprecipitation profiles of mutants versus wild-type RAD9

Studies have shown that RAD9 exists in multiple phosphorylated forms that may represent different functional states of the protein, affecting its interactions with other proteins in the DNA damage response pathways .

What are common issues when detecting RAD9 by Western blot and how can they be resolved?

When analyzing RAD9 by Western blot, it's important to remember that the protein exists in multiple phosphorylated forms, especially after DNA damage, which can lead to complex banding patterns . Validating band specificity using siRNA knockdown is highly recommended .

How can I measure RAD9 function in DNA damage repair pathways?

For functional assessment of RAD9 in DNA repair:

• γ-H2AX focus assay:

  • Compare γ-H2AX focus formation and resolution kinetics in RAD9-proficient vs. deficient cells

  • RAD9-deficient cells typically show delayed kinetics of focus appearance and disappearance after ionizing radiation

• Cell survival assays:

  • Measure survival after DNA-damaging agents (IR, UV, hydroxyurea)

  • RAD9 deficiency leads to enhanced S- and G2-phase-specific cell killing after IR exposure

• Chromosomal repair assays:

  • Analyze metaphase spreads for chromosomal aberrations

  • RAD9-deficient cells show increased chromosome end-to-end associations and telomere loss

• Homologous recombination assay:

  • Use DR-GFP reporter system to measure HR repair efficiency

  • RAD9 inactivation results in decreased HR repair

• Non-homologous end joining (NHEJ) assay:

  • In vitro NHEJ assay using cell extracts with immunodepleted or siRNA-knocked down RAD9

These assays have demonstrated that RAD9 plays critical roles in multiple DNA repair pathways, with some pathway-specific functions mediated through interactions with proteins like MLH1 .

What strategies can be used to differentially study the checkpoint versus repair functions of RAD9?

To distinguish between RAD9's checkpoint and repair functions:

• Separation-of-function mutants:

  • The S160A mutation specifically disrupts RAD9-MLH1 interaction and MMR function without affecting checkpoint control

  • Other point mutations may specifically affect checkpoint functions while preserving repair activities

• Cell-cycle synchronized studies:

  • Synchronize cells in different cell cycle phases

  • Analyze RAD9's repair functions in specific phases (e.g., HR repair predominantly in S and G2)

• Pathway-specific assays:

  • Use specific repair substrates/reporters to measure individual repair pathways

  • Combine with RAD9 mutants or depletion strategies

• Interaction partner analysis:

  • Study RAD9 interactions with checkpoint proteins (e.g., TopBP1/Dpb11) vs. repair proteins (e.g., MLH1, RAD51)

  • Use co-IP or PLA to detect these interactions under different conditions

• Temporal analysis:

  • Study early (typically checkpoint) vs. late (typically repair) responses after DNA damage

  • Use time-course experiments with RAD9 antibodies to track localization and interactions

Research has demonstrated that some RAD9 functions in repair can be separated from its checkpoint functions, as observed with the S160A mutation that specifically affects MMR activity without impacting S/M or G2/M checkpoint controls .

How is RAD9 involved in B cell function and antibody generation?

RAD9 plays critical roles in B cell biology:

• B cell proliferation: RAD9 is required for normal B cell proliferative responses. RAD9-deficient B cells show impaired growth responses and enhanced DNA lesions .

• Immunoglobulin class switch recombination (CSR):

  • RAD9 is essential for efficient CSR

  • RAD9-deficient mice show impaired immunoglobulin production in response to immunization

  • The absence of RAD9 leads to deficient Ig class switch recombination in B cells

• Genome integrity:

  • RAD9 maintains genomic stability during the programmed DNA modifications required for antibody generation

  • These include V(D)J recombination, CSR, and somatic hypermutation

  • RAD9 likely functions at the intersection of DNA damage detection and repair during these processes

Research using conditional knock-out mice with RAD9 specifically deleted in B cells has demonstrated that RAD9 plays dual roles in generating functional antibodies and in maintaining genome integrity during B cell development .

What is known about RAD9's transcriptional regulation activities?

Beyond its DNA repair functions, RAD9 has transcriptional regulatory activities:

• p53-like functions: RAD9 can bind p53 consensus sequences in promoter regions, including the p21 promoter, and can transactivate p21 expression .

• Regulation of multiple genes: Microarray studies in p53-deficient H1299 cells overexpressing RAD9 have identified numerous genes whose RNA levels are increased, suggesting a broader role for RAD9 in transcriptional regulation .

• Mechanism of action:

  • RAD9 can form protein-DNA complexes with specific DNA sequences

  • Electrophoretic mobility shift assays (EMSAs) have demonstrated that RAD9 binds DNA directly

  • RAD9-DNA complexes can be supershifted with specific RAD9 antibodies

• Target gene functions: The genes regulated by RAD9 are involved in various cellular processes including cell cycle progression, apoptosis, DNA repair, and signal transduction .

These findings suggest that RAD9 functions not only in DNA damage detection and repair but also in the transcriptional response to DNA damage, potentially regulating genes necessary for cellular recovery.

How can advanced imaging techniques be combined with RAD9 antibodies for studying DNA damage responses?

Advanced imaging techniques with RAD9 antibodies can provide unique insights:

• Super-resolution microscopy:

  • STORM or PALM imaging with RAD9 antibodies to visualize nanoscale distribution at damage sites

  • Dual-color super-resolution to study co-localization with repair factors with nanometer precision

• Live-cell imaging:

  • Combined with fluorescently tagged repair factors to study dynamics

  • FRAP (Fluorescence Recovery After Photobleaching) to measure mobility and residence time of RAD9 at damage sites

• FRET-based approaches:

  • Study RAD9 interactions with partners like MLH1 or RAD51

  • Measure conformational changes in the 9-1-1 complex upon DNA damage

• ChIP-seq combined with imaging:

  • Correlate genome-wide binding profiles with nuclear localization patterns

  • Validate ChIP-seq findings using immunofluorescence with RAD9 antibodies

• Single-molecule tracking:

  • Study the dynamics of individual RAD9 molecules at DNA damage sites

  • Measure binding/unbinding kinetics in living cells

These advanced approaches can reveal how RAD9 is dynamically recruited to different types of DNA damage and how it coordinates the assembly of repair complexes at these sites.