This website uses cookies to ensure you get the best experience on our website.
- Table of Contents
CDK8 · Western blot design guide
Design a Western Blot for CDK8
Real validated CDK8 Western blot protocols, expected-band and isoform facts, troubleshooting for weak or shifted signal, and recommended anti-CDK8 WB antibodies. Everything you need to plan the experiment before you commit precious samples.
Last reviewed: May 2026 · Scientific review: Boster Bio technical team
CDK8 Western Blot Experimental Design Guide
Expected bands, validated protocols, controls and antibodies — the at-a-glance facts below, then the full design guide.
Must know before running
| Expected band | ~53.3 kDa | |
| Observed band | 53 kDa | |
| Gel | 10–12% | |
| Negative control | siRNA / KO lysate |
Important caveats
Reasons your observed band may differ from the expected size.
| PTM | — | |
| Caveat | Alternative splicing isoforms | |
| Regulation | Apical junction | |
| Isoform | 2 isoform(s) |
Section 1
Real Curated CDK8 Western Blot Protocols
Literature-validated Western blot parameters for CDK8 — gel percentage, transfer, blocking, antibody incubation and detection, extracted from published methods.
| Sample / lysate | human Hela , Lane 2: human K562 , Lane 3: human Jurkat , Lane 4: human Caco-2 , Lane 5: human HEK293 . After electrophoresis, proteins were transferred to a nitrocellulose membrane at 150 mA for 50-90 minutes. Blocked the membrane with 5% non-fat milk/TBS for 1.5 hour at RT. The membrane was incubated with rabbit anti-CDK8 antigen affinity purified polyclonal antibody (Catalog # A01493-1) at 0.5 μg/mL overnight at 4°C, then washed with TBS-0.1%Tween 3 times with 5 minutes each and probed with a goat anti-rabbit IgG-HRP secondary antibody at a dilution of 1:5000 for 1.5 hour at RT. The signal is developed using an Enhanced Chemiluminescent detection (ECL) kit (Catalog # EK1002) with Tanon 5200 system. A specific band was detected for CDK8 at approximately 53 kDa. The expected band size for CDK8 is at 53 kDa |
| Gel % | 10–12% |
| Load | 30 ug |
| Transfer | nitrocellulose membrane, 150 mA, 50–90 min |
| Membrane | nitrocellulose |
| Blocking | 5% non-fat milk / TBS, 1.5 h RT |
| Primary antibody | 0.5 µg/mL |
| Primary incubation | overnight at 4 °C |
| Secondary antibody | goat anti-rabbit IgG-HRP, 1:5000 |
| Wash | TBS-0.1% Tween, 3 × 5 min |
| Detection | ECL |
| Exposure / imaging | Tanon 5200 |
| Observed band | 53 kDa |
Section 2
What Is the Expected CDK8 Western Blot Band Size?
CDK8 has a 53.3 kDa predicted mass and runs at the matching 53 kDa observed band, since it lacks glycosylation, disulfides, or cleavage events that would shift its size.
| single sharp band at ~53 kDa | matches the predicted CDK8 monomer mass with no glycosylation, disulfide crosslinking, or precursor cleavage to shift mobility |
| faint doublet or closely spaced second band near 53 kDa | reflects co-expression of the two annotated CDK8 splice isoforms (1 and 2) |
| signal present in nuclear or whole-cell lysate | consistent with CDK8's nuclear localization as a kinase module component of the Mediator complex |
| no very high-molecular-weight band near the intact Mediator complex size | the Mediator complex is held together non-covalently and dissociates under denaturing SDS-PAGE, so CDK8 runs as a free monomer |
| no diffuse high-molecular-weight smear above 53 kDa | CDK8 has no annotated glycosylation sites, so heterogeneous glycoform smearing is not expected |
💡Expected CDK8 appearanceExpect a single sharp band at 53 kDa, matching both CDK8's predicted 53.3 kDa mass and its empirically observed band, since it carries no glycosylation, disulfide crosslinks, or cleavage events that would shift its apparent size.
| Predicted mass (53.3 kDa) | sets the baseline migration position, which matches the empirically observed 53 kDa band closely |
| Alternative splicing (isoforms 1 and 2) | can yield a minor secondary band or doublet if both isoforms are co-expressed, though no distinct per-isoform mass is defined |
| Mediator complex association (non-covalent) | does not add apparent mass on a denaturing gel because SDS-PAGE dissociates the complex, leaving CDK8 as a monomer |
| Nuclear localization | keeps CDK8 retained in nuclear/whole-cell lysates rather than depleted into secreted fractions, supporting consistent signal |
| Absence of glycosylation and disulfide modifications | keeps the band sharp and single rather than smeared or shifted upward |
| Situation | Likely cause | Next action |
|---|---|---|
| Multiple bands | detection of both annotated splice isoforms 1 and 2, or non-specific antibody cross-reactivity | compare band pattern across cell lines and confirm specificity with a knockdown or knockout control |
| Band higher than expected | incomplete denaturation leaving residual Mediator complex or aggregate interactions intact | ensure thorough boiling and reducing sample preparation with fresh denaturing loading buffer |
| Band lower than expected | proteolytic degradation during nuclear lysate preparation, since CDK8 has no protective modifications like glycosylation | add protease inhibitors and keep lysates cold throughout nuclear extraction |
| Weak or no signal | low endogenous CDK8 expression or incomplete solubilization of the nuclear compartment | use a dedicated nuclear extraction or RIPA buffer with sonication to fully release nuclear protein |
| No band in lysate | cytoplasmic-only fractionation that excludes the nuclear pool where CDK8 resides | switch to whole-cell lysis or a nuclear extraction protocol to capture nuclear CDK8 |
Experiment evidence
Western blot images showing CDK8 band
A01493-1 · CDK8
← swipe / scroll for more images →
Real WB data behind the band-size expectations in this section.
Sample controls for CDK8 Western blot
🧪For positive controls for CDK8 in Western blot, you can use HeLa whole-cell lysate, since CDK8 is a nuclear kinase subunit of the Mediator complex expressed broadly across cultured human cell lines.
Positive control: HeLa cell lysate
Negative control: ubiquitously expressed; use siRNA knockdown or KO line
Loading controls: Run GAPDH, β-actin, and a total-protein stain (e.g., stain-free gel, Ponceau S, or REVERT) alongside as loading controls.
⚠️Feasibility: No HPA tissue expression data is available for CDK8, so no confirmed positive or negative tissue can be named; confirm signal specificity with an siRNA knockdown or CRISPR KO lysate rather than relying on tissue selection.
Comprehensive Human Protein Atlas IHC scoring per tissue. Rows are taken directly from the HPA tissue chart — click any row's HPA link to view the source.
Positive expression · recommended positive controls
| Tissue | Cell type | Level | Evidence | Source |
|---|
Undetected expression · recommended negative controls
| Tissue | Cell type | Level | Evidence | Source |
|---|
Section 3
Advanced CDK8 Western Blot Tips
Deeper troubleshooting and optimisation questions for CDK8, answered from its protein features.
Why does CDK8 run close to its predicted 53 kDa mass?
UniProt lists no signal peptide, propeptide, glycosylation, or modified residues for CDK8, so the mature protein retains its full unmodified length. This explains why the observed ~53 kDa band matches the calculated 53.3 kDa mass closely, unlike proteins carrying PTMs or cleavage that shift migration.
Do CDK8 isoforms appear as separate Western blot bands?
UniProt annotates two CDK8 isoforms (1 and 2) arising from alternative splicing. Depending on which region differs between them, a second band of altered molecular weight may appear alongside the canonical 53 kDa band. Confirm results with an antibody targeting a region common to both isoforms, or one specific to your isoform of interest.
How to optimize blocking for detecting CDK8?
CDK8 is a nuclear kinase and Mediator complex subunit, typically lower in relative abundance than cytoplasmic housekeeping proteins. Use 5% non-fat milk or BSA in TBST and extend blocking to about 1 hour to reduce background without masking the target band at 53 kDa.
What transfer method to use for CDK8 Western blot?
At ~53 kDa, standard wet transfer or semi-dry transfer is sufficient (e.g., 100V for 60-90 minutes wet, or the manufacturer-recommended semi-dry protocol) onto PVDF or nitrocellulose. CDK8 does not require the extended transfer times or lower voltages needed for high molecular weight proteins.
How to quantify CDK8 without confusing isoform signal?
Because CDK8 has two annotated isoforms, select a loading control unrelated to transcriptional regulation, such as GAPDH or beta-actin, and quantify only the band matching the expected 53 kDa mass. This avoids conflating isoform-specific signal with total CDK8 protein levels during densitometry.
What explains unexpected higher molecular weight CDK8 bands?
CDK8 functions as part of the large multi-subunit Mediator complex. Incomplete denaturation or insufficient reducing conditions can leave residual complex interactions intact, producing higher-order bands above 53 kDa. Ensure samples are fully denatured with SDS and a reducing agent before loading to resolve monomeric CDK8.
Is CDK8 kinase activity detectable as a band shift?
UniProt lists no modified residues for CDK8, so standard Western blot will not resolve phosphorylation-based shifts in the CDK8 band itself. Since CDK8 is a Ser/Thr kinase within the Mediator complex, assess its activity through downstream phospho-substrate antibodies rather than expecting a shift in CDK8's own migration.
Boster reagents
Best CDK8 Western Blot Antibodies
BosterBio's CDK8 antibodies are among the best-performing WB antibodies on the market — well cited, thoroughly validated, and orthogonally cross-validated against negative tissues and complementary methods.
Real WB data
Anti-CDK8 Antibody Picoband®
Cat # A01493-1
The recommended anti-CDK8 antibodies below are top-performing, highly cited reagents for Western blot, rigorously validated with clear specific bands and cross-checked against negative tissue and complementary detection methods to confirm target specificity.
Which to pick: Only one CDK8 antibody is catalogued, A01493-1, which includes an actual Western blot validation image showing a specific band, so it is the one to use for your CDK8 WB experiments.
Source: BosterBio CDK8 gene-info card — filtered to Western-blot-capable antibodies; each card shows that product's actual WB validation figure.
References
- UniProt Consortium. UniProt entry P49336.
- Human Protein Atlas. CDK8 tissue expression.