Antisense RNA

Antisense RNA is RNA complementary to a specified sense transcript or part of it, allowing antiparallel base pairing with that target. Sense and antisense are relational labels: the target and strand orientation must be specified. Antisense molecules can occur naturally or be produced experimentally, and complementary pairing can influence transcript processing, stability or access to translation machinery.^[ref]

For an original sequence example, a target segment $5^{\prime }\text{-}\mathrm{AUGCC}\text{-}{3}^{\prime }$ pairs with $3^{\prime }\text{-}\mathrm{UACGG}\text{-}{5}^{\prime }$. Written in the usual $5^{\prime }$-to-$3^{\prime }$ direction, the antisense sequence is $5^{\prime }\text{-}\mathrm{GGCAU}\text{-}{3}^{\prime }$. Merely replacing each target letter by its complement without reversing the written direction gives a different sequence.

A tomato experiment expressed Antisense RNA directed against 1-aminocyclopropane-1-carboxylate synthase, a precursor-forming enzyme in ethylene biosynthesis. Ripening was inhibited, and supplying ethylene or propylene reversed the effect. The intervention and rescue linked altered expression to a physiological signal pathway, rather than treating ripening and ethylene production as a simple correlation.^[ref]

Complementarity alone is not a quantitative prediction of suppression. Target accessibility, expression levels and the cellular machinery determine the outcome. An Antisense RNA construct, an observed change in target protein and an observed phenotype therefore provide different pieces of evidence.