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Short answer
Beta-actin (b-actin) is the cytoplasmic actin protein encoded by the human ACTB gene. It is 375 amino acids long and about 42 kDa (41,737 Da for the human protein in UniProt). It forms the actin filaments of the cytoskeleton, which support cell structure, motility and signalling. In the lab, anti-beta-actin antibodies are most often used to check protein loading on western blots, and that use has well-documented limits.
Who this is for: researchers and lab staff who need the protein’s size, role and identifiers in one place, and who must decide whether beta-actin is a sound loading control for a given blot. This page is general reference, not a protocol.
Definition and scope: gene, protein and aliases
“Beta actin”, “b-actin”, “β-actin”, “ACTB” and “Actin, cytoplasmic 1” all point at the same human gene product. The names differ only by whether they refer to the gene or the protein.
| Item | Value (human) | Source |
|---|---|---|
| Gene symbol | ACTB (“actin beta”), chromosome 7, band 7p22.1 | NCBI Gene 60 |
| Recommended protein name | Actin, cytoplasmic 1 (alternative name: beta-actin) | UniProt P60709 |
| Length | 375 amino acids | UniProt P60709 |
| Mass | 41,737 Da (about 42 kDa) | UniProt P60709 |
| Gene aliases | BKRNS, BNS, BRWS1, CSMH, DDS1, PS1TP5BP1, THC8 | NCBI Gene 60 |
NCBI describes ACTB as one of six actin proteins and one of two ubiquitously expressed nonmuscle cytoskeletal actins. It also notes numerous pseudogenes, which matters when designing PCR primers. UniProt lists the initiator methionine as removed, so the mature chain starts at residue 2, and Asp-2 is N-acetylated.
What is the kDa of beta-actin?
About 42 kDa. UniProt gives the calculated mass of the human protein as 41,737 Da. On a gel, band position depends on the gel system, the marker used and any post-translational modifications, so report the marker and gel chemistry rather than assuming an exact figure.
What is the main function of actin in cells?
Per UniProt, cytoplasmic actin 1 forms filaments and cross-linked networks in the cytoplasm, cycling between monomeric G-actin and filamentous F-actin. NCBI summarises the roles as cell motility, structure, integrity and signalling. UniProt also records nuclear roles in transcription and DNA damage repair, a contribution to assembly of the gamma-tubulin ring complex, and a place in the ACTR1A/ACTB filament around which the dynactin complex is built. It is found in the cytoplasm (cytoskeleton), the nucleus and cytoplasmic mRNP granules, with “low tissue specificity” of expression.
What is the purpose of beta-actin?
Biologically, it is a structural and functional component of the cell’s cytoskeleton (above). Experimentally, it serves two common purposes: as a target in studies of cytoskeleton and cell motility, and as an internal reference (“loading control”) on western blots, because it is abundant and widely expressed. Ubiquitous expression does not guarantee that a protein is constant across your samples or behaves linearly on your blot, as the next sections show.
What is the purpose of the anti-actin antibody test?
In research, an anti-actin (anti-beta-actin) antibody detects actin on a blot or in a stained sample, usually to confirm that comparable protein was loaded in each lane before target-protein levels are compared. It is a reagent-based laboratory check, not a diagnostic test for a person. Clinical autoantibody testing is a separate subject and is not covered here.
Beta-actin as a western blot loading control: a sourced checklist
Normalization corrects for errors in sample loading, electrophoresis, transfer and sample concentration. A Thermo Fisher technical note on quantitative chemiluminescent western blotting states that an accurate loading control should show a linear relationship between sample load and signal intensity in all experimental conditions. Use these points when deciding whether beta-actin qualifies:
- Check saturation. The same note reports that housekeeping proteins, including beta-actin, GAPDH and alpha-tubulin, have been shown to saturate at common lysate loading amounts (for example 30 to 50 µg per well), after which signal levels off and no longer tracks protein amount. Saturation in the control or the target prevents accurate quantitation.
- Keep the load low if beta-actin is the control. Chen and Xu (Electrophoresis 2015;36:2046-9, PMID 26033488) found beta-actin is often overloaded in routine blots, concluded that less than 2 µg of total protein should be loaded when it is the loading control, and advised against reprobing the membrane with a beta-actin antibody.
- Test linearity for your own samples. In the Thermo Fisher note’s HeLa lysate experiment (10 to 50 µg per lane), the linearity of total-protein signal gave R2 = 0.9990, versus 0.8851 for beta-actin, 0.9438 for GAPDH and 0.8332 for alpha-tubulin. This is one vendor’s experiment with its own reagents, so treat it as an illustration of why linearity should be checked, not as a universal ranking.
- Consider total-protein normalization. The same note presents total protein normalization as an alternative to housekeeping proteins. See housekeeping protein vs. total-protein normalization for the comparison.
Where it matters for labs and supply decisions
When a lab or core facility specifies anti-beta-actin antibodies, secondary reagents or blotting kits, the loading-control strategy should be fixed first: the antibody’s species and clonality, the detection chemistry and the lysate load all affect whether the signal stays linear. For related reading, see how to interpret western blot results, secondary antibodies for western blotting and western blot kits. Follow the antibody manufacturer’s datasheet for dilutions and conditions.
Common misunderstandings
- “Housekeeping” does not mean constant. Wide expression (UniProt: low tissue specificity) is not the same as unchanged expression across treatments, and not the same as a linear blot response.
- Beta-actin is not the only actin. NCBI notes ACTB is one of six actin proteins and one of two nonmuscle cytoskeletal actins; check antibody specificity in your sample type.
- Gene name versus protein name. ACTB (italic gene symbol) and beta-actin or “Actin, cytoplasmic 1” (protein) are the same entity at different levels.
- An actin band is not proof of equal loading. A strong, saturated band can look even when loads differ.
FAQ
What is the purpose of beta actin?
It is a cytoskeletal protein involved in cell structure, motility and signalling, and a common western blot loading control.
What is the purpose of the anti-actin antibody test?
It detects actin in a lab sample, typically to confirm even protein loading between lanes. It is a research reagent check, not a clinical diagnostic.
What is the kDa of beta actin?
About 42 kDa (41,737 Da calculated for the 375-residue human protein, UniProt P60709).
What is the main function of actin in cells?
Forming filaments and networks that support cell shape, movement and signalling; cytoplasmic actin also has nuclear roles in transcription and DNA repair.
What is the ACTB gene’s full name?
“Actin beta”, located at 7p22.1 on human chromosome 7 (NCBI Gene 60).
Sources
- UniProt entry P60709, ACTB_HUMAN, Actin, cytoplasmic 1 (rest.uniprot.org/uniprotkb/P60709.txt), read 2026-11-07.
- NCBI Gene ID 60, ACTB actin beta (ncbi.nlm.nih.gov/gene/60), read 2026-11-07.
- Thermo Fisher Scientific technical note on quantitative chemiluminescent western blotting (PDF), read 2026-11-07.
- Chen W, Xu WH. beta-Actin as a loading control: Less than 2 µg of total protein should be loaded. Electrophoresis 2015;36(17):2046-9. doi:10.1002/elps.201500138; PubMed 26033488, read 2026-11-07.
