Biotin-streptavidin matrix

Figure 7.4. Isolation of poly-A+ RNA by biotin-streptavidin affinity matrix. Poly-A+ RNA is captured as a hybrid between poly-A+ RNA and biotinylated oligo(dT) by streptavidin matrix. Most mRNAs carry poly-A+ stretch at their 3 end, and hence poly A-containing RNA can be enriched substantially by this affinity capture method. Poly-A+ RNA can be eluted from the beads by low salt or water. The eluted RNA can be ethanol precipitated.

Antibodies or other binding proteins (e.g., protein A, biotin-avidin, and biotin-streptavidin) adsorbed or covalently attached to an insoluble matrix (e.g., plastic beads, inside surface of a plastic tube or microwell, and magnetic beads)... 

Affinity-based proteomics. In affinity-based proteomics, a compound of interest is immobilized to the solid surface by means of functional groups (e.g., NHj) or using the biotin-streptavidin interaction. Cell lysate that contains the target proteins is then incubated with the immobilized compound and this leads to enrichment of proteins on the matrix (1). Stringent washing removes proteins that unspecifically bind to the solid surface. Bound proteins are then released from the matrix by elution (e.g., with an excess of unmodified compound) or by heating... 

Fig. 8.6. By utilizing a streptavidin-coupled immobilized matrix or gel-shift PAGE, the affinity tag biotin allows the RNA catalysts to be captured and separated from the noncatalytic RNA.

The specific binding of RNA or proteins to beads can be accomplished by various methods. RNA may be tethered to a matrix by incorporating biotin, a 244-Dalton vitamin, randomly in the RNA during transcription (see Section 2.3.2) so that the RNA subsequently can be attached to an avidin- or streptavidin column... 

Much of the nontarget nucleic acid can be excluded by a sequence-specific preprocessing step, of which many are under development. The most common example of this protocol is sequence recognition by a biotinylated probe, followed by separation by interaction between the biotin and a streptavidin-labeled matrix. This procedure has been used for microRNA [83], mRNA [84,85], and ssDNA enrichment from total nucleic acid samples [86,87]. Other unique systems include the use of gold nanoparticles for SNP detection [88], and superparamagnetic particles coupled to a PCR-ELISA detection modality for hepatitis C virus cDNA detection [89] or environmental DNA sample cleanup [90]. 

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