Sense (molecular biology) 5504842 221829299 2008-06-26T08:16:43Z SpBot 7016748 robot Adding: [[de:Codogener Strang]] {{Mergefrom|Coding strand|date=December 2007}} '''Sense''', when applied in a [[molecular biology]] context, is a general concept used to compare the polarity of [[nucleic acid]] molecules, such as [[DNA]] or [[RNA]], to other nucleic acid molecules. Depending on the context within molecular biology, sense may have slightly different meanings. ==DNA sense== [[molecular biology|Molecular biologists]] call a DNA single strand or sequence '''sense''' (or positive sense) if an RNA version of the same sequence is translated or translatable into protein, and they call its complement '''antisense''' (or negative sense). Sometimes the phrase '''coding strand''' is encountered; however, protein coding and [[non-coding RNA]]'s can be transcribed similarly from both strands, in some cases being transcribed in both directions from a common promoter region, or being transcribed from within [[introns]], on both strands. ===Antisense DNA=== [[Image:Antisensedna.jpg|Schematic showing how antisense DNA strands can interfere with protein translation.|thumb|250px|right]] '''Antisense''' molecules interact with [[Complementarity (molecular biology)|complementary]] strands of [[nucleic acid]]s, modifying expression of [[gene]]s. Some regions within a double strand of [[DNA]] code for genes, which are usually instructions specifying the order of [[amino acid]]s in a [[protein]] along with regulatory sequences, [[splicing]] sites, noncoding [[intron]]s 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, [[antisense mRNA|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)[http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=10807004&query_hl=12] 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 therapy|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 mRNA|antisense RNA]] molecules naturally, which interact with complementary mRNA molecules and inhibit their expression. ==Ambisense== A genome which contains both positive-sense and negative-sense is said to be '''ambisense'''. [[Bunyaviridae|Bunya viruses]] have 3 fragments containing both positive-sense and negative-sense sections; [[arenavirus]]es are also ambisense, having 2 fragments which are mainly negative-sense except for part of the 5' ends of the large and small segments of their genome. ==Antisense mRNA== {{main|Antisense mRNA}} '''Antisense''' mRNA is an mRNA transcript that is complementary to [[endogenous]] mRNA. In other words, it is a non-coding strand complementary to the coding sequence of mRNA; this is similar to negative-sense viral RNA. Introducing a [[transgene]] coding for antisense mRNA is a technique used to block expression of a gene of interest. Radioactively-labelled antisense mRNA can be used to show the level of transcription of genes in various cell types. Some [[Nucleic_acid_analogues|alternative antisense structural types]] are being experimentally applied as [[antisense therapy]], with at least one antisense therapy approved for use in humans. ==RNA sense== In [[virology]], the [[genome]] of a [[RNA virus]] can be said to be either '''positive-sense''', also known as a "plus-strand", or '''negative-sense''', also known as a "minus-strand". In most cases, the terms ''sense'' and ''strand'' are used interchangeably, making such terms as ''positive-strand'' equivalent to ''positive-sense'', and ''plus-strand'' equivalent to ''plus-sense''. Whether a virus is positive-sense or negative-sense can be used as a basis for classifiying viruses. ===Positive-sense=== Positive-sense (5' to 3') viral RNA signifies that a particular viral RNA sequence may be directly [[Translation (genetics)|translated]] into the desired viral proteins. Therefore, in positive-sense RNA viruses, the viral RNA genome can be considered viral mRNA, and can be immediately translated by the host cell. Unlike negative-sense RNA, positive-sense [[RNA]] is of the same sense as mRNA. Some viruses (e.g. [[Coronaviridae]]) have positive-sense genomes which can act as mRNA and be used directly to synthesise proteins without the help of a complementary RNA intermediate. Because of this, these viruses do not need to have an RNA transcriptase packaged into the [[virion]]. ===Negative-sense=== Negative-sense (3' to 5') viral RNA is complementary to the viral mRNA and thus must be converted to positive-sense RNA by an [[RNA polymerase]] prior to translation. Negative-sense RNA (like DNA) has a [[nucleotide sequence]] complementary to the [[mRNA]] that it encodes. Like [[DNA]], this RNA cannot be translated into [[protein]] directly. Instead, it must first be transcribed into a positive-sense RNA which acts as an mRNA. Some viruses ([[Influenza]], for example) have negative-sense genomes and so must carry an [[RNA polymerase]] inside the [[virion]]. ==See also== *[[DNA]] *[[Virus#Replication|Viral replication]] *[[RNA Virus]] *[[Antisense therapy]] *[[Transcription (genetics)]] *[[Translation (genetics)|Translation]] ==References== *Prescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3 *[http://www.google.com/search?q=cache:vvi2xZeH-LQJ:www.ivis.org/advances/Carter/Part1Chap3/chapter.asp Viral replication and genetics] - Google's cache of a page from the International Veterinary Information Service *[http://arjournals.annualreviews.org/doi/abs/10.1146%2Fannurev.bi.60.070191.003215 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. [[Category:DNA]] [[Category:RNA]] [[Category:Genetics]] [[Category:Molecular biology]] [[Category:Virology]] [[Category:Microbiology]] [[de:Codogener Strang]] [[es:Antisentido]] [[fr:Antisens]] [[zh:義 (分子生物學)]]