* The meaning of sub-Virus Asian virus (subviruses) is a more simple analog viruses, with only a nucleic acid does not have the protein, or only with the protein but not with nucleic acids, the tiny plants and animals can be infected by pathogens. He does not have the complete structure of virus-like virus known as sub-viruses, including viroids, satellite rna, prions. * Sub-structure of the virus
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Viroid
The early 20th century, 70, American scholar and his colleagues in the study diener potato spindle tuber pathogen, the pathogen-free virus particles were observed and antigenicity of phenol and other organic solvents is not sensitive to heat (70 ℃ ~ 75 ℃), on stable high-speed centrifugation (note the low molecular weight), enzyme-sensitive characteristics of rna. All these features show that the pathogen is not a virus, but a free small molecule rna. Thus proposed a new concept - like virus (viroid). Before this concept was put forward, it was believed that, by the protein and nucleic acid polymer composition of two biological system, the life of the original system, and never suspect the virus is a complex system, the minimum limit of life. Class is a class of viruses that can infect some plant pathogenic single-stranded closed circular of rna molecules. Classes of small viral genome, the molecular weight of 1 × 10 5 th power. Like virus has been sequenced more than 100 variants, the rna molecules are rod-like structure, the number of base pairs of double-stranded region and does not match the single-stranded circular areas arranged in phases. They share a common characteristic is the central place in the secondary structure elements have a conservative area. Like virus is usually 246 to 399 nucleotides. Such as potato spindle tuber viroid (potato spindle tuber viroid, pstvd, vd is used to distinguish between the virus) is composed of 359 nucleotides units of a covalently closed circular rna molecules, about 50a ~ 70nm. Not all classes mrna rna virus activity does not encode any polypeptide, its replication is through the host catalytic rna polymerase ii, conducted in the nucleus rna rna to direct transcription. Like virus caused the infection independently, in nature there are different classes virulent virus strains. pstvd the attenuated strain is only about 10% cut, while the virulent strain can be cut 70% to 80%. Like viruses can all the way through the mechanical damage to spread by contact with farming tools for the mechanical transmission is spread in nature, the main way this disease. Some like virus, such as pstvd can directly spread by seed and pollen. Virus-like virus disease symptoms with no obvious difference between most of the typical symptoms of virus disease can also be caused by a class of viruses. Like virus infection with a long incubation period, and showed persistent infection. Different classes have different host range viruses. If pstvd sensitive to hundreds of host plants, in addition to the Solanaceae, there Boraginaceae, Campanulaceae, Caryophyllaceae, Compositae and so on. Cracked skin of citrus-like virus (citrus exocortis viroid, cevd) the host range to be narrower than pstvd, but can also be infected mandarin families Asteraceae, Solanaceae, Cucurbitaceae and other 50 species of plants. Like virus found that half of the 20th century an important event in biology, virology horizons broadened. It may exist in the further study of the class of plant virus disease has opened up a new direction.
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Prion
Sb prusiner by American scholars found the causative agent of scrapie - prion (1982), and won the 1997 Nobel Prize in Physiology and Medicine. PrP (virino) infection also known as protein factor (prion, proteinaceous infectious agents), is a smaller than a virus, has infected only with the hydrophobic nature of protein molecules. Purification of the infectious agent called prion protein (prion protein, prp). With prp sc pathogenic prions, said that it has anti-protease hydrolysis capacity k can be specifically in the infected brain tissue, showing amyloid form. Many fatal central nervous system of mammals are related to prion related degeneration, such as human kuru (kuru, a tremor disease), Keyashizheng (creutzfeldt-jakob disease, cjd, a kind of early Alzheimer's disease), death familial insomnia (fatal familiar insomnia, ffi) and animal scrapie (scrapie), bovine spongiform encephalopathy (bovine spongiform encephalopathy, bse mad cow disease, also known as mad cow disease), cat spongiform encephalopathy (feline spongifoem encephalopathy, fse) and so on. Normal human and animal cells have dna coding prp genes whose expression products expressed by prp c, relative molecular mass of 33 ~ 35kda. Prp c expression in normal cells and sheep scrapie prp sc as isomers, prp c and prp sc has the same amino acid sequence, prp c 43% and 3% α-helix β-sheet, and about prp sc 34% 43% α-helix and β-sheet. Several fold to reduce the solubility of prp sc, increase resistance to the protease. Since the prp sc is a protein and does not contain any nucleic acid, then it is human or animal body and how is copied, how it spread? Prusiner other miscellaneous dimerization mechanism proposed hypothesis, both prp sc infected with single-molecule properties , from prp c gradually change the conformation of single molecules to form prp sc monomer, in the middle through the prp c - prp sc hybrid dimers, and then into prp sc-prp c. In this process, there are unknown protein (protein x) may play an adjustment of prp c into shape or maintain the role of prp sc. The dimer dissociation and the release of a new prp sc, so continue to "copy" down. Biology of prions found in a shock, because it is now recognized as the "central dogma" that is the direction of flow of genetic information is "dna / rna → protein" contrary to the traditional concept. pursiner and others to clarify the pathogenesis of scrapie prion conformation is due to changes in disease. This discovery opened up a new area of etiology, may be the pathogenesis of other transmissible spongiform encephalopathies and the cause of nature, provide a new way of thinking, the development of biological science is of great significance.
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To be virus and satellite rna
80 years since the 20th century, one after another from the pile in Australia smoke, alfalfa, clover Belladonna and underground discovered four new plant viruses. Within the capsid proteins of these viruses contain two kinds of rna molecules, a molecular weight of 1.5 × 10 6 da of linear rna 1, the other is the molecular weight of about 10 5 da-like virus-like cyclic rna 2, Such molecules are known to be rna 2 virus (virusoid). There are two proposed molecular structure of the virus, one ring rna 2, the second is linear rna 3. rna 2 and rna 3 rna molecule is presented in the same two different configurations, which may be rna 2 rna 3 precursor, which rna 2 cyclization by rna 3 formed. To be the virus in the nucleotide composition, size and secondary structure of the class are similar to the virus in the biological nature but with satellite rna (satellite rna) the same, such as: ① alone is not infectious, must depend on the helper virus to the infection and replication, the replication requires a helper virus-encoded rna-dependent rna polymerase. ② The rna do not have the coding ability, need to use the helper virus coat protein and helper virus genomes with the rna virus particles together within the same package. ③ and proposed satellite rna virus can interfere with helper virus replication. ④ and proposed satellite rna virus rna virus genome with the aid comparison, there is no sequence homology between them. According to the proposed satellite rna and the common characteristics of these viruses, and now there are many scholars are collectively referred to as satellite or satellite virus rna.