Are Enzymes Necessary For Positive Single-Stranded Rna?

Positive-sense single-stranded RNA (ssRNA) viruses are a key aspect of the infectious cycle of the virus, as they produce necessary proteins for replication. These proteins include the RNA-dependent RNA polymerase (RdRp), which is responsible for synthesizing new viral RNA from the virus’s own RNA template. Two types of RNA viruses in the family Narnaviridae consist of a single molecule of non-encapsidated positive-strand RNA of 2.3-2.9 kb, which encodes a single protein of 80-104 kDa with amino acid.

RNA viruses have RNA as their genetic material and their nucleic acid is usually single-stranded RNA or double-stranded RNA. Important human pathogenic RNA viruses include HIV-1, which is a lentivirus with an RNA genome formed by two copies of a single-stranded, positive-sense RNA. Coronaviruses are positive-strand RNA viruses with an unusually large genome of ~30 kb and express an RNA-dependent RNA polymerase and a cohort of other replication.

Infectious virions of (+)RNA viruses transmit the viral genome as a single-stranded, messenger-sense RNA that is replicated intracellularly via a double-stranded RNA. Design and development of SARS-CoV-2 specific direct-acting antiviral drugs can be made possible by targeting conserved enzymes such as main protease or 3C-like protease (Mpro).

The packaging of genomic RNA in positive-sense single-stranded RNA viruses is a key part of the viral infectious cycle, but this step is not fully understood. All positive-strand RNA viruses encode an RNA-dependent RNA polymerase (RdRP), which is central to the phylogenetic evolution of the virus. The positive-sense RNA molecule then acts as viral mRNA, which is translated into protein.

What is the difference between a (+) strand and a (-) strand of RNA?

Quick Reference. 1. in a single-stranded RNA virus, a plus strand is one having the same polarity as viral mRNA and containing codon sequences that can be translated into viral protein. A minus strand is a noncoding strand that must be copied by an RNA-dependent RNA polymerase to produce a translatable mRNA. 2. in a single-stranded DNA virus, a plus strand is one contained in the virus particle or any strand having the same base sequence. A minus strand has a base sequence complementary to the plus strand; mRNA can be transcribed from the minus strand. See Baltimore classification of viruses, hairpin ribozyme.

Do positive-sense viruses need RdRP?

Consequently, the virions of positive-sense RNA viruses do not contain viral RdRP. In general, these virions are constructed more simply than those of dsRNA and negative-sense ssRNA viruses, or compared with many positive-sense RNA viruses infecting nonplant hosts.

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What is an example of a positive-sense single stranded RNA virus?

Eight virus families, including Picornaviridae, Caliciviridae, Hepeviridae, Flaviviridae, Togaviridae, Arteriviridae, and Coronaviridae, are known to infect vertebrates with single-stranded, positive-sense RNA genomes. These viruses use their own genome as messenger RNA (mRNA) to synthesize polyproteins that are cleaved into individual proteins by viral or cellular proteases. They also possess the genetic information for the synthesis of an RNA-dependent RNA polymerase, which transcribes the positive RNA strand and complementary negative RNA strands as intermediate products of genome replication.

The classification of these viruses into different taxonomic families depends on factors such as the number, size, position, and orientation of viral genes in the RNA molecule, the number of different polyproteins synthesized during viral infection, and the existence of an envelope as a virion component. Picornaviruses were first discovered in 1898 by Friedrich Loeffler and Paul Frosch, who described the pathogen of foot-and-mouth disease (FMD) as a filterable agent. In 1909, Karl Landsteiner and Emil Popper published an article identifying a virus as the pathogen of poliomyelitis, a disease first described by Jacob von Heine in 1840 and later by Oskar Medin.

These viruses can cause a cytopathic effect in human embryonic cell cultures, but their actual characterization as poliovirus was only ascertained by Herdis von Magnus and co-workers in 1955. The classification of these viruses into different taxonomic families depends on factors such as the number, size, position, and orientation of viral genes, the number of different polyproteins synthesized during viral infection, and the presence of an envelope as a virion component.

What important enzyme for viral lifecycle is carried in (+) ssRNA retrovirus virions?

If the viral genome is RNA, a different mechanism must be used. There are three types of RNA genome: dsRNA, positive (+) single-strand (+ssRNA) or negative (−) single-strand RNA (−ssRNA). If a virus has a +ssRNA genome, it can be translated directly to make viral proteins. Viral genomic +ssRNA acts like cellular mRNA. However, if a virus contains a −ssRNA genome, the host ribosomes cannot translate it until the −ssRNA is replicated into +ssRNA by viral RNA-dependent RNA polymerase (RdRP) (see Figure 5). The RdRP is brought in by the virus and can be used to make +ssRNA from the original −ssRNA genome. The RdRP is also an important enzyme for the replication of dsRNA viruses, because it uses the negative strand of the double-stranded genome as a template to create +ssRNA. The newly synthesized +ssRNA copies can then be translated by cellular ribosomes.

Figure 5. RNA viruses can contain +ssRNA that can be directly read by the ribosomes to synthesize viral proteins. Viruses containing −ssRNA must first use the −ssRNA as a template for the synthesis of +ssRNA before viral proteins can be synthesized.

An alternative mechanism for viral nucleic acid synthesis is observed in the retrovirus es, which are +ssRNA viruses (see Figure 6). Single-stranded RNA viruses such as HIV carry a special enzyme called reverse transcriptase within the capsid that synthesizes a complementary ssDNA (cDNA) copy using the +ssRNA genome as a template. The ssDNA is then made into dsDNA, which can integrate into the host chromosome and become a permanent part of the host. The integrated viral genome is called a provirus. The virus now can remain in the host for a long time to establish a chronic infection. The provirus stage is similar to the prophage stage in a bacterial infection during the lysogenic cycle. However, unlike prophage, the provirus does not undergo excision after splicing into the genome.

What is the difference between positive and negative stranded RNA?

Single-stranded RNA viruses can be classified into negative-sense and positive-sense, or ambisense RNA viruses, based on the sense or polarity of their RNA. Positive-sense viral RNA is similar to mRNA and can be translated by the host cell, while negative-sense viral RNA is complementary to mRNA and requires conversion by an RNA polymerase. Purified RNA of a positive-sense virus can cause infection, but may be less infectious than the whole virus particle. Ambisense RNA viruses resemble negative-sense RNA viruses but also translate genes from the positive strand.

Picornaviruses are a common viral positive-strand RNA virus that infect humans. They belong to the Picornaviridae family and are non-enveloped, positive-stranded RNA viruses with an icosahedral capsid. The genome RNA is unusual due to a protein on the 5′ end used as a primer for transcription by RNA polymerase. Picornaviruses are separated into various genera and include many important pathogens of humans and animals.

Enteroviruses infect the enteric tract, while rhinoviruses primarily infect the nose and throat. Enteroviruses replicate at 37°C, while rhinoviruses grow better at 33°C due to their lower temperature. Enteroviruses are stable under acid conditions, allowing them to survive exposure to gastric acid, while rhinoviruses are acid-labile, limiting their infections to the nose and throat.

What is the difference between positive-sense RNA and negative sense RNA?

Single-stranded RNA viruses can be classified into negative-sense and positive-sense, or ambisense RNA viruses, based on the sense or polarity of their RNA. Positive-sense viral RNA is similar to mRNA and can be translated by the host cell, while negative-sense viral RNA is complementary to mRNA and requires conversion by an RNA polymerase. Purified RNA of a positive-sense virus can cause infection, but may be less infectious than the whole virus particle. Ambisense RNA viruses resemble negative-sense RNA viruses but also translate genes from the positive strand.

Picornaviruses are a common viral positive-strand RNA virus that infect humans. They belong to the Picornaviridae family and are non-enveloped, positive-stranded RNA viruses with an icosahedral capsid. The genome RNA is unusual due to a protein on the 5′ end used as a primer for transcription by RNA polymerase. Picornaviruses are separated into various genera and include many important pathogens of humans and animals.

Enteroviruses infect the enteric tract, while rhinoviruses primarily infect the nose and throat. Enteroviruses replicate at 37°C, while rhinoviruses grow better at 33°C due to their lower temperature. Enteroviruses are stable under acid conditions, allowing them to survive exposure to gastric acid, while rhinoviruses are acid-labile, limiting their infections to the nose and throat.

What is the difference between positive and negative single stranded RNA?

Single-stranded RNA viruses can be classified into negative-sense and positive-sense, or ambisense RNA viruses, based on the sense or polarity of their RNA. Positive-sense viral RNA is similar to mRNA and can be translated by the host cell, while negative-sense viral RNA is complementary to mRNA and requires conversion by an RNA polymerase. Purified RNA of a positive-sense virus can cause infection, but may be less infectious than the whole virus particle. Ambisense RNA viruses resemble negative-sense RNA viruses but also translate genes from the positive strand.

Picornaviruses are a common viral positive-strand RNA virus that infect humans. They belong to the Picornaviridae family and are non-enveloped, positive-stranded RNA viruses with an icosahedral capsid. The genome RNA is unusual due to a protein on the 5′ end used as a primer for transcription by RNA polymerase. Picornaviruses are separated into various genera and include many important pathogens of humans and animals.

Enteroviruses infect the enteric tract, while rhinoviruses primarily infect the nose and throat. Enteroviruses replicate at 37°C, while rhinoviruses grow better at 33°C due to their lower temperature. Enteroviruses are stable under acid conditions, allowing them to survive exposure to gastric acid, while rhinoviruses are acid-labile, limiting their infections to the nose and throat.

Which viruses need RdRp?

RdRp is an essential protein encoded in the genomes of most RNA-containing viruses that lack a DNA stage, including SARS-CoV-2. Some eukaryotes also contain RdRps, which are involved in RNA interference and differ structurally from viral RdRps.

Viral RdRps were discovered in the early 1960s from studies on mengovirus and polio virus when it was observed that these viruses were not sensitive to actinomycin D, a drug that inhibits cellular DNA-directed RNA synthesis. This lack of sensitivity suggested the action of a virus-specific enzyme that could copy RNA from an RNA template.

Structure and replication elongation mechanism of a RdRp.

Which enzyme is required by (-) ssRNA viruses for their replication?

RdRp enzymes DNA viruses replicate their genomes using DNA polymerase enzymes and transcribe their mRNA using DNA-dependent RNA polymerase enzymes. Both (+) and (−) ssRNA viruses replicate and transcribe their genomes using RdRp enzymes (Fig. 3. 1).

Summary. Regardless of their genetic constitution, viral genomes are replicated, expressed, and assembled in association with living host cells. These entities do not undergo division, but rather generate new particles through the assembly of preformed components. Some viruses go further by modifying cellular metabolism to create a more favorable environment for viral gene expression. In a few instances, these clever strategies also facilitate escape from the host’s defense responses. The process of replication is typically divided into the phases of attachment, entry, uncoating, genome replication and expression, assembly, maturation, and finally, egress or release from the host cell. In this chapter, we address genome replication and expression, including the multiple strategies that serve to control gene expression and ensure preferential propagation of the virus.

Keywords: Frameshifting, polyprotein, ribosome shunting, virus gene expression, preferential virus replication.

Nature’s stern discipline enjoins mutual help at least as often as warfare.

What enzyme is typically used to replicate (+) ssRNA viruses?

RdRp enzymes Both (+) and (−) ssRNA viruses replicate and transcribe their genomes using RdRp enzymes (Fig. 3. 1).

Summary. Regardless of their genetic constitution, viral genomes are replicated, expressed, and assembled in association with living host cells. These entities do not undergo division, but rather generate new particles through the assembly of preformed components. Some viruses go further by modifying cellular metabolism to create a more favorable environment for viral gene expression. In a few instances, these clever strategies also facilitate escape from the host’s defense responses. The process of replication is typically divided into the phases of attachment, entry, uncoating, genome replication and expression, assembly, maturation, and finally, egress or release from the host cell. In this chapter, we address genome replication and expression, including the multiple strategies that serve to control gene expression and ensure preferential propagation of the virus.

Keywords: Frameshifting, polyprotein, ribosome shunting, virus gene expression, preferential virus replication.

Nature’s stern discipline enjoins mutual help at least as often as warfare.

Which of the following applies to (+) ssRNA viruses?

The correct answer is d) They can be directly translated by the ribosome. Viral RNA-dependent RNA polymerase (RdRP), also known as replicase, is required for replication rather than for the initial translation process.