= Antisense RNA
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<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 (biology)> machinery.<Molecular Biology of the Cell, 4th edition by Bruce Alberts and others>[Chapter7, Control of Gene Expression: antisense RNA and post-transcriptional regulation]{ref}
For an original sequence example, a target segment $5'\text{-}\mathrm{AUGCC}\text{-}3'$ pairs with $3'\text{-}\mathrm{UACGG}\text{-}5'$. Written in the usual $5'$-to-$3'$ direction, the antisense sequence is $5'\text{-}\mathrm{GGCAU}\text{-}3'$. 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.<Reversible inhibition of tomato fruit senescence by antisense RNA by P. W. Oeller and others>[1991 abstract: antisense intervention and reversal by external gas]{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.
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