Sense (molecular biology)

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Sense, when applied in a molecular biology context, is a general concept used to compare the polarity of nucleic acid molecules, particularly RNA, to other nucleic acid molecules. Depending on the context within molecular biology, sense may have slightly different meanings.

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 viral RNA signifies that a particular viral RNA sequence may be directly 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 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.

DNA sense

Molecular biologists call a DNA single strand or sequence sense if an RNA version of the same sequence is translated or translatable into protein, and they call its complement antisense. 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.

Ambisense

A genome which contains both positive-sense and negative-sense is said to be ambisense. Bunya viruses have 3 fragments containing both positive-sense and negative-sense sections; arenaviruses 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

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 alternative antisense structural types are being experimentally applied as antisense therapy, with at least one antisense therapy approved for use in humans.

See also

References

  • Prescott, L. (1993). Microbiology, Wm. C. Brown Publishers, ISBN 0-697-01372-3
  • Viral replication and genetics - Google's cache of a page from the International Veterinary Information Service

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