antisense

 

DNA or RNA manipulated in a laboratory so that its components (nucleotides) form a complementary copy of normal, or “sense,” messenger RNA (mRNA; see nucleic acid). Antisense techniques are used to deactivate disease-causing or undesirable genes so that they cannot produce harmful or unwanted proteins. (Conventional drugs bind directly with disease-causing protein molecules, but their imperfect specificity may lead them to bind with other protein molecules, resulting in unwanted side effects. Antisense molecules are extremely specific.) In some applications of this technique, the antisense nucleic acid segment is inserted into an inactivated or nonvirulent virus, then introduced into the cell. The antisense segment pairs with the mRNA, preventing the synthesis of protein by the mRNA. Antisense has applications in agricultural biotechnology, where it has been used to deactivate the gene that causes softening in tomatoes, and in medicine, especially in cancer and antiviral therapy. See also gene therapy.

It has been suggested that this article or section be merged into Sense (molecular biology). (Discuss)

Antisense molecules interact with complementary strands of nucleic acids, modifying expression of genes.

Some regions within a double strand of DNA code for genes, which are usually instructions specifying the order of amino acids in a protein along with regulatory sequences, splicing sites, noncoding introns and other complicating details. For a cell to use this information, one strand of the DNA serves as a template for the synthesis of a complementary strand of RNA. The template DNA strand is called the transcribed strand with antisense sequence and the mRNA transcript is said to be sense sequence (the complement of antisense). Because the DNA is double-stranded, the strand complementary to the antisense sequence is called non-transcribed strand and has the same sense sequence as the mRNA transcript (though T bases in DNA are substituted with U bases in RNA).

DNA strand 1: sense strand

DNA strand 2: antisense strand (copied to)→ RNA strand (sense)

Many forms of antisense have been developed and can be broadly categorized into enzyme-dependent antisense or steric blocking antisense.

Enzyme-dependent antisense includes forms dependent on RNase H activity to degrade target mRNA, including single-stranded DNA, RNA, and phosphorothioate antisense. The R1 plasmid hok/sok system is an example of mRNA antisense regulation process, through enzymatic degradation of the resulting RNA duplex. Double stranded RNA acts as enzyme-dependent antisense through the RNAi/siRNA pathway, involving target mRNA recognition through sense-antisense strand pairing followed by target mRNA degradation by the RNA-induced silencing complex (RISC).

Steric blocking antisense (RNase-H independent antisense)[1] interferes with gene expression or other mRNA-dependent cellular processes by binding to a target sequence of mRNA and getting in the way of other processes. Steric blocking antisense includes 2'-O alkyl (usually in chimeras with RNase-H dependent antisense), peptide nucleic acid (PNA), locked nucleic acid (LNA) and Morpholino antisense.

Antisense nucleic acid molecules have been used experimentally to bind to mRNA and prevent expression of specific genes. Antisense therapies are also in development; in the USA, the Food and Drug Administration (FDA) has approved a phosphorothioate antisense oligo, fomivirsen (Vitravene), for human therapeutic use.

Cells can produce antisense RNA molecules naturally, which interact with complementary mRNA molecules and inhibit their expression.

References

Annual Review of Biochemistry Vol. 60: 631-652 (Volume publication date July 1991) (doi:10.1146/annurev.bi.60.070191.003215) Antisense RNA Y Eguchi, ­T Itoh, and ­J Tomizawa

Weiss, B. (ed.): Antisense Oligodeoxynucleotides and Antisense RNA : Novel Pharmacological and Therapeutic Agents, CRC Press, Boca Raton, FL, 1997.

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