Sense (molecular biology)

The polarity of a nucleic acid described in virology, the ratio of a single-stranded viral genome to the reading direction of the later messenger RNA (mRNA), which is derived from this genome. In general, a nucleic acid, in the 5 ' → 3' direction (the direction of reading of the ribosome during translation ) has the correct sequence of base triplets for the subsequent protein as a positive - stranded or sense is referred to ( reasonable, sensible ). In a single-stranded (ss, single -stranded ) RNA and single-stranded DNA with positive polarity corresponds to the base sequence in the 5 ' → 3' direction of the subsequent mRNA. In a ssRNA and ssDNA with a negative polarity, the genome is complementary to each mRNA. The discrimination of the polarity of the nucleic acids results from the fact that in a double-stranded nucleic acid (dsRNA or dsDNA) in each case only one strand of the transcription of the mRNA is used, while the second strand only complementary, so to speak, " a mirror image upside down " the genetic information reproduces.

If a virus, there are three types of polarity of the genome: the ( ) polarity (sense), the ( - ) polarity ( antisense ) and the presence of ( ) - and (- ) polarity on the same strand ( ambisense ). This distinction is for the taxonomic classification of viruses of great importance and reflects different replication strategies of viruses resist.

( ) Polarity (sense)

For viruses with single-stranded ( ) ssRNA genome as equivalent to the sequence of bases that of the later mRNA. For viruses with ( ) ssRNA, which corresponds to an mRNA, it is directly translated by ribosomes into protein ( see figure). All viruses with a ( ) ssRNA genome must code for its own RNA-dependent RNA polymerase which must be read in a first step of penetrating into the cell the RNA strand. The proliferation of the viral ssRNA is via a complementary ( - ) strand as template for a further ( )- strands. Known examples of the very many viruses with ( ) ssRNA are the Flaviviridae (e.g., hepatitis C virus ) and the Picornaviridae.

In the ( rare ) ( ) - ssDNA viruses, the synthesis of the mRNA is carried out on the codogenic complementary (-) strand, which is only present during the replication in the cell. Previously, the single-strand DNA is accompanied by cellular DNA polymerases, to form a double strand. A ( ) ssDNA can be found in the Inoviridae Bakteriophagenfamilien and Microviridae ( circular ( ) ssDNA ) plant viruses as well as the the Nanoviridae ( segmented ( ) ssDNA).

( - ) Polarity ( antisense )

At a (-) ssRNA always takes a completion to a double-stranded RNA, the newly formed complementary RNA strand of the mRNA and can be translated into corresponding protein. Eukaryotic cells do not have the enzyme that catalyzes the complementation of a ssRNA to a dsRNA strand. Therefore, viruses have a (- ) ssRNA genome have built into their virion is always at least one molecule of a viral RNA polymerase, which can then initiate viral protein and RNA synthesis at the onset of virus replication in the cell. Viruses with ssRNA negativsträngiger make up the majority of viral species. These include viruses from the order Mononegavirales (which owe their name to the partial negative negativity of non- segmented genome), as well as the family of Orthomyxoviridae (eg, influenza virus genera ).

When (-) ssDNA virus mRNA is synthesized directly on this line or previously completed by cellular DNA polymerases to form a double strand. The complementary DNA strand corresponds to the base sequence of the mRNA. A (-) ssDNA genome is found in the Geminiviridae ( circular (-) ssDNA plant viruses ), and the genus Gyrovirus the family Circoviridae ( circular (-) ssDNA, Vertebrate ).

( / - ) Polarity ( ambisense )

A special form of a mixing sense and antisense genome, there are some ssRNA and ssDNA viruses. Here lie on a single nucleic acid strand before both polarities of what has been called ambisense polarity or ( / - ) indicates polarity. The genes are then distributed to at least two nucleic acid strands, one of which occasionally has to be generated only as a complementary sequence. The two different polarity regions are either independently transcribed into mRNA ( in antisense regions, according to their reading direction ) or can be read directly as mRNA (sense ) regions respectively correspond to the mRNA. The ambisense polarity can not be the simultaneous or alternate presence of individual ( ) - strands be confused ( at Parvoviridae for example ) in the viral genome and (-). Not with the presence of open reading frames in both directions of a double stranded nucleic acid ( for example, in the Polyomaviridae ).

Viruses with ssRNA ambisense are the Arenaviridae (eg Lassa fever virus) and with partial ambisense polarity the Bunyaviridae. A ambisense - ssDNA is found in the genus Circovirus of the family Circoviridae.

Swell

• SJ Flint, LW Enquist, VR Racaniello and AM Skalka: Principles of Virology. Molecular Biology, Pathogenesis, and Control of Animal Viruses. 2nd edition, ASM Press Washington, D.C. 2004, ISBN 1-55581-259-7 pp. 67ff

• Virology