shRNA, short hairpin RNA, is the expressed form of RNA interference: a hairpin transcribed from a DNA construct inside the cell and processed into a small interfering RNA that silences its target. Because it is delivered as DNA, buying shRNA means buying a plasmid, a viral vector or a pooled library rather than an oligo, and the decisions are about vector, promoter and validation. This page explains the formats and points at the plasmid preparation comparison for the material you will need to make.
shRNA against siRNA
A synthetic siRNA is transfected directly and gives a transient knockdown that fades as cells divide. An shRNA is expressed from a promoter on a plasmid or an integrated lentiviral vector, so the knockdown persists, can be selected for, and can be made inducible. The cost structure follows: siRNA is a per-target oligo purchase, shRNA is a per-construct cloning and plasmid purchase, with the vector cost spread across every experiment that uses it.
Plasmid, lentiviral and library formats
A plasmid shRNA suits transient transfection in easy cell lines. A lentiviral shRNA construct, packaged into particles, reaches primary and non-dividing cells and integrates for a stable line. A pooled shRNA library targets thousands of genes in one vector pool for a screen, and its quality is a matter of representation: every hairpin present at a similar abundance in the plasmid pool, which is exactly what a large, careful plasmid preparation protects. Each format needs a different amount and grade of plasmid DNA.
Validating a hairpin before you scale
Not every designed hairpin silences. Order or clone several per target, test knockdown at the protein level, and check for the off-target and toxicity effects the RNA interference literature warns about. Public repositories publish validated hairpin sequences and the vectors they sit in, which is the sensible place to start before a custom design. Only after validation is it worth ordering the larger plasmid preparation or the lentiviral packaging for the stable line.
What to buy from a vendor and at what grade
For plasmid transfection, a research grade preparation with endotoxin reduction is enough. For lentiviral packaging, a transfection grade preparation with a specified supercoiled fraction pays for itself in titre. For a pooled library, the preparation must preserve representation, so ask the vendor how they amplify and whether they report hairpin distribution. The plasmid preparation pages on this site record each vendor's published prices by scale and grade, verified and dated.
Questions people ask about shrna
What is the difference between shRNA and siRNA?
siRNA is a synthetic double-stranded RNA delivered directly for a transient knockdown; shRNA is expressed from a DNA construct and processed in the cell, giving a persistent, selectable knockdown.
Can I buy shRNA ready made?
Yes: validated shRNA plasmids and lentiviral constructs for most human and mouse genes are sold by repositories and vendors, and pooled libraries are sold for screens.
What promoter drives an shRNA?
Usually a polymerase III promoter such as U6 or H1 for constitutive expression, or an engineered inducible version of one for switchable knockdown.
What grade of plasmid do I need for lentiviral packaging?
Transfection grade, endotoxin free, with a high supercoiled fraction; it is the single biggest lever on viral titre after the packaging cells themselves.