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FlexiTube siRNA

For efficient RNAi analysis one gene at a time
  • Cost-effective siRNA enables analysis of more genes
  • Optimal solutions for every gene
  • Innovative design minimizes the risk of off-target effects
  • Easy to search for and order siRNA at GeneGlobe

Two different FlexiTube products are available: FlexiTube siRNA and FlexiTube GeneSolution.

FlexiTube siRNA is a cost-effective solution for RNAi analysis of small numbers of genes. siRNAs are provided in 5 nmol or 20 nmol amounts for human, mouse, or rat genes, or in economical 1 nmol amounts for human and mouse genes.

FlexiTube GeneSolution is a gene-specific package of 4 preselected siRNAs (1 nmol) for a target gene. FlexiTube GeneSolutions enable researchers to use multiple siRNAs for each target ensuring reliable results. FlexiTube siRNA and FlexiTube GeneSolutions are designed using innovative HP OnGuard siRNA Design and are available at QIAGEN's GeneGlobe Web portal.

Buy Products

Cat No./ID: 1027415
FlexiTube siRNA (1 nmol)
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1 nmol siRNA delivered in tubes
Cat No./ID: 1027416
FlexiTube GeneSolution
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siRNA GeneSolution details
Cat No./ID: 1027417
FlexiTube siRNA (5 nmol)
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5 nmol siRNA delivered in tubes
Cat No./ID: 1027418
FlexiTube siRNA (20 nmol)
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20 nmol siRNA delivered in tubes
Cat No./ID: 1027419
FlexiTube siRNA (20 nmol)
Go to GeneGlobe
20 nmol siRNA with modification options delivered in tubes
The FlexiTube siRNA is intended for molecular biology applications. This product is not intended for the diagnosis, prevention, or treatment of a disease.

Product Details

Performance guarantee

FlexiTube siRNA comes with a one-time-only replacement offer. If several FlexiTube siRNAs for the same target gene are ordered and at least 2 of them do not provide ≥70% target gene knockdown, QIAGEN will provide 2 additional siRNAs free of charge, once only. You will be asked to provide supporting data, demonstrating that the siRNA failed to knock down the target gene by at least 70% at the mRNA level under appropriate transfection conditions. Supporting data should include transfection efficiency data, quantitative silencing data, and data showing ≥70% knockdown of a positive control. This offer is valid for up to 6 months after the date of delivery.

Thousands of experimentally verified siRNAs

Thousands of our human siRNAs have been experimentally verified by real-time RT-PCR analysis and shown to provide at least 70% knockdown. For these verified siRNAs, experimental details and information about the level of knockdown achieved are provided in GeneGlobe. These experimentally verified siRNAs are the result of the world's largest siRNA validation project, which was carried out by QIAGEN scientists. To find out more about this project, consult the publication Krueger, U. et al. (2007) Insights into Effective RNAi Gained from Large-Scale siRNA Validation Screening. Oligonucleotides 17, 237.

Cutting-edge siRNA design

Advances in the siRNA design process ensure that QIAGEN's highly innovative and sophisticated HP OnGuard siRNA Design delivers potent and specific siRNA. siRNAs are designed using neural-network technology based on an extremely large set of data from RNAi experiments. siRNA design is then checked for homology to all other sequences of the genome using an up-to-date, nonredundant sequence database and a proprietary homology analysis tool. HP OnGuard siRNA Design incorporates many unique and advanced features (see table).

HP OnGuard siRNA Design features
FeatureDescription References
Neural-network technology siRNA design uses the BioPredsi neural-network, which is based on an extremely large RNAi data set. 1-3
The world's largest siRNA validation project The design process was reinforced and improved by data from this project, in which QIAGEN scientists proved the effectiveness of thousands of siRNAs, were used to . A large number of druggable genome siRNAs have been proven to provide at least 70% knockdown during this project. 4
Homology analysis Analysis uses a proprietary tool and an up-to-date, nonredundant sequence database.
Affymetrix GeneChip analysis Genomewide analysis enabled development of siRNA design improvements that minimize off-target effects.
Up-to-date siRNA target sequences Current data from NCBI databases ensure accurate design.
Asymmetry siRNAs are designed with unequal stabilities of the base pairs at the 5' ends. This enables the antisense strand, which is less tightly bound at its 5' end, to enter RISC, while the sense strand is degraded. Asymmetry produces highly functional siRNAs and reduces the risk of off-target effects caused by the incorrect strand entering RISC. 5, 6
3' UTR/seed region analysis Analysis uses intelligently weighted, multi-parameter searches for matches of the seed region of the siRNA antisense strand with the 3' untranslated region of unintended mRNA targets (see text for further explanation). 7-12
SNP avoidance The RefSNP database is used to exclude siRNAs that span single nucleotide polymorphisms (SNPs). This increases siRNA potency, as an siRNA spanning a SNP will vary in its effectiveness.
Interferon motif avoidance siRNAs are screened for multiple sequence motifs known to result in an interferon response. siRNAs with such motifs are rejected. 13, 14
1. Huesken, D. et al. (2005) Design of a genome-wide siRNA library using an artificial neural network. Nat. Biotechnol. 23, 995.
2. Mukherji, M. et al. (2006) Genome-wide functional analysis of human cell-cycle regulators. Proc. Natl. Acad. Sci. 103, 14819.
3. Matveeva, O. et al. (2007) Comparison of approaches for rational siRNA design leading to a new efficient and transparent method. Nucleic Acids Res. 35, e63.
4. Krueger, U. et al. (2007) Insights into effective RNAi gained from large-scale siRNA validation screening. Oligonucleotides 17, 237.
5. Aza-Blanc, P. et al. (2003) Identification of modulators of TRAIL-induced apoptosis via RNAi-based phenotypic screening. Mol. Cell 12, 627.
6. Schwarz, D.S. et al. (2003) Asymmetry in the assembly of the RNAi enzyme complex. Cell 115, 199.
7. Farh, K.K. et al. (2005) The widespread impact of mammalian microRNAs on mRNA repression and evolution. Science 310, 1817.
8. Grimson, A. et al. (2007) MicroRNA targeting specificity in mammals: determinants beyond seed pairing. Mol. Cell 27, 91.
9. Jackson, A.L. et al. (2003) Expression profiling reveals off-target gene regulation by RNAi. Nat. Biotechnol. 21, 635.
10. Lewis, B.P., Burge, C.B., and Bartel, D.P. (2005) Conserved seed pairing, often flanked by adenosines, indicates that thousands of human genes are microRNA targets. Cell 120, 15.
11. Lim, L.P. et al. (2005) Microarray analysis shows that some microRNAs downregulate large numbers of target mRNAs. Nature 433, 769.
12. Saxena, S., Jónsson, Z.O., and Dutta, A. (2003) Small RNAs with imperfect match to endogenous mRNA repress translation. Implications for off-target activity of small inhibitory RNA in mammalian cells. J. Biol. Chem. 278, 44312.
13. Judge, A.D., Sood, V., Shaw, J.R., Fang, D., McClintock, K., and MacLachlan, I. (2005) Sequence-dependent stimulation of the mammalian innate immune response by synthetic siRNA. Nat Biotechnol. 23, 457.
14. Hornung, V. et al. (2005) Sequence-specific potent induction of IFN-alpha by short interfering RNA in plasmacytoid dendritic cells through TLR7. Nat Med. 11, 263. 
3' UTR/seed region analysis

Several studies have shown that off-target effects may be caused by matches of the seed region of the siRNA antisense strand with the 3' untranslated region of unintended mRNA targets (see table). The seed region comprises 6 nucleotides in positions 2–7 of the antisense siRNA strand of the siRNA duplex. Matches such as these can contribute to downregulation of unintended targets due to the siRNA mimicking the action of an miRNA. siRNA designed at QIAGEN is analyzed for 3' UTR/seed region complementarity using a proprietary set of 3' UTR sequences derived from the human, rat, and mouse RefSeq databases. Each siRNA is aligned against these sequences to check for any homology that could contribute to miRNA-like, off-target effects.

Matches of 6 out of 6 nucleotides of the siRNA seed region with an unrelated target 3' UTR sequence are common and it is not necessary or practical to eliminate siRNAs showing such matches. More rarely, seed region matches in combination with 10 or more bases of additional homology are observed in an siRNA sequence. Such homologies have greater potential to result in off-target effects, and where possible these siRNAs are rejected in favor of others with less significant homology to unintended target genes.

For some targets, it is not possible to select siRNAs that do not show any such homologies. In these cases, EntrezGene IDs of the unrelated genes that could be unintended targets of the siRNA are provided at GeneGlobe. Observation of this type of homology does not necessarily mean that these genes will be affected by the siRNA. However, they can be considered potential unintended targets for follow up analysis, if warranted. 


FlexiTube siRNA enables ordering of small numbers of siRNAs at cost-effective 1 nmol amounts (the minimum order is 4 siRNAs), or in 5 nmol and 20 nmol amounts. siRNAs are provided lyophilized in tubes.

FlexiTube GeneSolution for optimal gene-specific solutions

For a streamlined RNAi solution for your target gene, simply enter details of the human or mouse genes of interest at the GeneGlobe Web portal. The search results will display the FlexiTube GeneSolution, which is the 4 recommended siRNAs for each gene provided in 1 nmol amounts. Published guidelines recommend redundancy experiments to ensure accurate reporting of results from RNAi experiments (Echeverri, C.J. et al. (2006) Minimizing the risk of reporting false positives in large-scale RNAi screens. Nat. Methods. 3, 777; Echeverri, C.J. and Perrimon, N. (2006) High-throughput RNAi screening in cultured cells: a user’s guide. Nature Reviews Genetics 7, 373.). Redundancy experiments use several distinct siRNAs targeting different areas of the same mRNA to rule out off-target effects. An off-target phenotype is induced by the specific pattern of cross-silenced transcripts of an siRNA. Since this directly derives from the siRNA sequence, it is highly unlikely that several siRNAs with different sequences will share the same sequence-derived off-target effects. Confirming a phenotype with several distinct siRNAs is an easily applied and convincing way to show siRNA specificity. FlexiPlate GeneSolutions enable redundancy experiments for human and mouse genes. siRNAs are recommended by QIAGEN for each gene so that the optimal solution for your experiments is at your fingertips!

Full siRNA sequence information provided

All siRNAs are provided with siRNA sequence information at no extra charge. Full sequence disclosure provides information for analysis of experimental results and verification of knockdown. siRNA sequences can be included in research publications, if required.

Modification options

FlexiTube siRNAs in 20 nmol amounts are available with labels, including Alexa Fluor, fluorescein, rhodamine, Cy3, and Cy5 dyes, or modification options such as amino linkers, thio linkers, and phosphate modifications.


We recommend HiPerFect Transfection Reagent for low-throughput siRNA transfection and HiPerFect HTS Reagent for high-throughput siRNA transfection.


FlexiTube siRNA and FlexiTube GeneSolution are ideal for functional genomics or pathway analysis with small numbers of gene targets.

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