Picornaviridae: Difference between revisions
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[[Image:24314a.jpg|thumb|200px|right|Poliovirus, in the family picornaviridae. © [http://www.denniskunkel.com Dennis Kunkel Microscopy, Inc.]]] | |||
==Baltimore Classification== | ==Baltimore Classification== | ||
===Higher order taxa=== | ===Higher order taxa=== | ||
Virus; Picornaviridae | Virus; ssRNA positive-strand viruses, no DNA stage; Picornaviridae | ||
===Genera=== | ===Genera=== | ||
Enterovirus, Rhinovirus, Hepatovirus, Cardiovirus, | ''[[Enterovirus]]'', ''[[Rhinovirus]]'', ''[[Hepatovirus]]'', ''[[Apthovirus]]'', ''Cardiovirus'', ''Parechovirus'', ''Erbovirus'', ''Kobuvirus'', and ''Teschovirus'' | ||
==Description and Significance== | ==Description and Significance== | ||
The name "picornavirus" means " little RNA virus" (''pico'' means "very small" in Greek; ''pico'' + RNA virus). Picornaviruses are among the oldest viruses, dating back to 1400 B.C., when a temple record tells of poliovirus infections in ancient Egypt. Picornaviruses are also among the most diverse viruses, with over 200 serotypes causing infections such as Polio, Hepatitis A, and the common cold. Foot-and-Mouth Disease Virus (genus: Apthovirus), which causes infections in livestock, was one of the first viruses to be recognized; it was discovered by Loeffler and Frosch in 1898. | The name "picornavirus" means " little RNA virus" (''pico'' means "very small" in Greek; ''pico'' + RNA virus). Picornaviruses are among the oldest viruses, dating back to 1400 B.C., when a temple record tells of poliovirus infections in ancient Egypt. Picornaviruses are also among the most diverse viruses, with over 200 serotypes causing infections such as Polio, Hepatitis A, and the common cold. Foot-and-Mouth Disease Virus (genus: Apthovirus), which causes infections in livestock, was one of the first viruses to be recognized; it was discovered by Loeffler and Frosch in 1898. (sources: [http://www.stanford.edu/group/virus/picorna/2004flynn/Picornaviridae2.htm Flynn], Bedard) | ||
==Genome Structure== | ==Genome Structure== | ||
The picornavirus genome consists of a single molecule of linear, postitive(+)-sense, single-strand RNA. It is non-segmented. The complete genome is 7000-8500 nucleotides long. | The picornavirus genome consists of a single molecule of linear, postitive(+)-sense, single-strand RNA. It is non-segmented. The complete genome is 7000-8500 nucleotides long. The 5'-terminus of the genome has a long untranslated region 600-1200 bases in length, which is important in translation, virulence, and possibly encapsidation. There is a shorter untranslated region (50-100 bases in length) on the 3'-terminus, which is important in (-)strand-synthesis. The 5'-terminus untranslated region also has a "clover leaf" secondary structure known as the Internal Ribosome Entry Site (IRES), which distinguishes picornaviruses from other RNA viruses; this structure is important in translation and replication. The 5'-terminus is modified by a covalently-attached VPg protein (which takes the place of a cap), while the 3'-terminus is modified by polyadenylation. (sources: [http://phene.cpmc.columbia.edu/ICTVdB/00.052.htm ICTVdB], Bedard, [http://www.stanford.edu/group/virus/picorna/2004flynn/Picornaviridae2.htm Flynn]) | ||
==Virion Structure of a Picornavirus== | ==Virion Structure of a Picornavirus== | ||
Picornavirus virions consist of a non-enveloped, icosahedrally symmetric capsid. The capsid consists of 12 capsomers and has a diameter of 27- | Picornavirus virions consist of a non-enveloped, icosahedrally symmetric capsid. The capsid consists of 12 capsomers and has a diameter of 27-30 nm, which makes it one of the smallest of all viruses (thus the name "''pico''rnavirus"). The genome is tightly packed into the capsid. The capsid has four unique proteins: VP1, 2, 3, and 4. (sources: [http://phene.cpmc.columbia.edu/ICTVdB/00.052.htm ICTVdB], [http://www.stanford.edu/group/virus/picorna/2004flynn/Picornaviridae2.htm Flynn]) | ||
==Reproductive Cycle of a Picornavirus in a Host Cell== | ==Reproductive Cycle of a Picornavirus in a Host Cell== | ||
Using different cellular receptors (depending on the picornavirus), a picornavirus virion attaches to a host cell. Uncoating occurs, and the virus' RNA is released into the cytoplasm of the host cell through a membrane channel. Virus replication occurs entirely in the cytoplasm. The host cell's transcription processes are shut off to a degree that varies with different picornaviruses, while the IRES helps to make sure the virus' transcription is left untouched. Replication occurs. RNA is packaged into preformed capsids. Release of the virus occurs when cell lysis occurs (with the exception of Hepatits A, which is non-lytic and thus creates a more persistent infection). | Using different cellular receptors (depending on the picornavirus), a picornavirus virion attaches to a host cell. Uncoating occurs, and the virus' RNA is released into the cytoplasm of the host cell through a membrane channel. Virus replication occurs entirely in the cytoplasm. The host cell's transcription processes are shut off to a degree that varies with different picornaviruses, while the IRES helps to make sure the virus' transcription is left untouched. Replication occurs. RNA is packaged into preformed capsids. Release of the virus occurs when cell lysis occurs (with the exception of Hepatits A, which is non-lytic and thus creates a more persistent infection). (source: Bedard) | ||
==Viral Ecology & Pathology== | ==Viral Ecology & Pathology== | ||
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The mode of transmission, ecology, and pathology of picornaviruses vary greatly between the different genera. Interestingly, the genetics of virulence phenotypes of picornaviruses is poorly understood. According to [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16568900&query_hl=4&itool=pubmed_docsum Tracy et al.], "Picornaviruses do not have virulence genes per se, but the design of the capsid and how it interacts with the virus receptor expressed on the host cell surface, specific sequences within the nontranslated regions of the viral genome, as well as coding sequences that result in different protein sequences may all have a part in determining the virulence phenotype." | The mode of transmission, ecology, and pathology of picornaviruses vary greatly between the different genera. Interestingly, the genetics of virulence phenotypes of picornaviruses is poorly understood. According to [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16568900&query_hl=4&itool=pubmed_docsum Tracy et al.], "Picornaviruses do not have virulence genes per se, but the design of the capsid and how it interacts with the virus receptor expressed on the host cell surface, specific sequences within the nontranslated regions of the viral genome, as well as coding sequences that result in different protein sequences may all have a part in determining the virulence phenotype." | ||
==References | ==References== | ||
Bedard, Kristin M. and Bert L. Semler. "Regulation of picornavirus gene expression." ''Microbes and Infection'' 6.7 (2004): 702-713. | |||
[http://www | [http://www.stanford.edu/group/virus/picorna/2004flynn/Picornaviridae2.htm Flynn, Emily. Picornaviridae.] | ||
[http://phene.cpmc.columbia.edu/ICTVdB/00.052.htm ICTVdB - The Universal Virus Database, version 4. http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/] | [http://phene.cpmc.columbia.edu/ICTVdB/00.052.htm ICTVdB - The Universal Virus Database, version 4. http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/] | ||
[http://www. | [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=16568900&query_hl=4&itool=pubmed_docsum Tracy et al. "Evolution of virulence in picornaviruses." ''Curr Top Microbiol Immunol'' 299 (2006): 193-209.] | ||
Latest revision as of 00:32, 8 August 2010
A Viral Biorealm page on the family Picornaviridae
Baltimore Classification
Higher order taxa
Virus; ssRNA positive-strand viruses, no DNA stage; Picornaviridae
Genera
Enterovirus, Rhinovirus, Hepatovirus, Apthovirus, Cardiovirus, Parechovirus, Erbovirus, Kobuvirus, and Teschovirus
Description and Significance
The name "picornavirus" means " little RNA virus" (pico means "very small" in Greek; pico + RNA virus). Picornaviruses are among the oldest viruses, dating back to 1400 B.C., when a temple record tells of poliovirus infections in ancient Egypt. Picornaviruses are also among the most diverse viruses, with over 200 serotypes causing infections such as Polio, Hepatitis A, and the common cold. Foot-and-Mouth Disease Virus (genus: Apthovirus), which causes infections in livestock, was one of the first viruses to be recognized; it was discovered by Loeffler and Frosch in 1898. (sources: Flynn, Bedard)
Genome Structure
The picornavirus genome consists of a single molecule of linear, postitive(+)-sense, single-strand RNA. It is non-segmented. The complete genome is 7000-8500 nucleotides long. The 5'-terminus of the genome has a long untranslated region 600-1200 bases in length, which is important in translation, virulence, and possibly encapsidation. There is a shorter untranslated region (50-100 bases in length) on the 3'-terminus, which is important in (-)strand-synthesis. The 5'-terminus untranslated region also has a "clover leaf" secondary structure known as the Internal Ribosome Entry Site (IRES), which distinguishes picornaviruses from other RNA viruses; this structure is important in translation and replication. The 5'-terminus is modified by a covalently-attached VPg protein (which takes the place of a cap), while the 3'-terminus is modified by polyadenylation. (sources: ICTVdB, Bedard, Flynn)
Picornavirus virions consist of a non-enveloped, icosahedrally symmetric capsid. The capsid consists of 12 capsomers and has a diameter of 27-30 nm, which makes it one of the smallest of all viruses (thus the name "picornavirus"). The genome is tightly packed into the capsid. The capsid has four unique proteins: VP1, 2, 3, and 4. (sources: ICTVdB, Flynn)
Using different cellular receptors (depending on the picornavirus), a picornavirus virion attaches to a host cell. Uncoating occurs, and the virus' RNA is released into the cytoplasm of the host cell through a membrane channel. Virus replication occurs entirely in the cytoplasm. The host cell's transcription processes are shut off to a degree that varies with different picornaviruses, while the IRES helps to make sure the virus' transcription is left untouched. Replication occurs. RNA is packaged into preformed capsids. Release of the virus occurs when cell lysis occurs (with the exception of Hepatits A, which is non-lytic and thus creates a more persistent infection). (source: Bedard)
Viral Ecology & Pathology
The mode of transmission, ecology, and pathology of picornaviruses vary greatly between the different genera. Interestingly, the genetics of virulence phenotypes of picornaviruses is poorly understood. According to Tracy et al., "Picornaviruses do not have virulence genes per se, but the design of the capsid and how it interacts with the virus receptor expressed on the host cell surface, specific sequences within the nontranslated regions of the viral genome, as well as coding sequences that result in different protein sequences may all have a part in determining the virulence phenotype."
References
Bedard, Kristin M. and Bert L. Semler. "Regulation of picornavirus gene expression." Microbes and Infection 6.7 (2004): 702-713.
ICTVdB - The Universal Virus Database, version 4. http://www.ncbi.nlm.nih.gov/ICTVdb/ICTVdB/
