Which viruses replicate in the nucleus

The functional roles of non-structural protein NS5A are varied, including biogenesis of viral replication factories, viral replication and assembly of viral particles Bonamassa et al. As described for many viruses, the HCV NS5A protein affects host interferon responses by interfering with transcriptional regulation of relevant genes. The host cell nucleus is essential to retrovirus replication as the reverse transcribed DNA is integrated into the host genome where it is transcribed by the host machinery.

Rice et al. Previous work by the group had shown nuclear trafficking of Gag is required for efficient encapsidation of gRNA.

The current article Rice et al. Their work raises the possibility that Gag localizes to the nucleus and associates with transcription factories to gain access to nascent unspliced viral RNA in order to capture it for encapsidation.

Herpes viruses, enteroviruses, and flaviviruses comprise majority of the known neurotrophic viruses. Interestingly, despite their very different genomes and diverse replication cycles, many have very similar pathogenic mechanisms. DNA viruses all replicate in the nucleus except for the pox virus, which replicates in the cytoplasm.

RNA viruses all replicate in the cytoplasm except for the inflenza virus and retroviruses, which replicate in the nucleus. Live attenuated vaccines are dangerous to give to immunocompromised patients. There are about 21 families and 65 genera of DNA viruses. The phylogenetic relationships between most viruses, including DNA viruses, are not well understood.

Poxviridae is a family of viruses. Human, vertebrates, and arthropods serve as natural hosts. There are currently 69 species in this family, divided among 28 genera, which are divided into two subfamilies. Diseases associated with this family include smallpox.

Poxviridae viral particles virions are generally enveloped external enveloped virion- EEV , though the intracellular mature virion IMV form of the virus, which contains different envelope, is also infectious. The virion is exceptionally large—around nm in diameter and nm in length.

The replication of poxvirus is unusual for a virus with double-stranded DNA genome dsDNA because it occurs in the cytoplasm, although this is typical of other large DNA viruses. Poxvirus encodes its own machinery for genome transcription, a DNA dependent RNA polymerase, which makes replication in the cytoplasm possible.

Key Points From the perspective of the virus, the purpose of viral replication is to allow production and survival of its kind. Most double-stranded DNA viruses replicate within the host cell nucleus, including polyomaviruses, adenoviruses, and herpesviruses—poxviruses, however, replicate in the cytoplasm. Adenoviruses and herpes viruses encode their own replication factors.

Polyomaviruses Polyomaviridae is a family of viruses whose natural hosts are primarily mammals and birds. Replication Prior to genome replication, the processes of viral attachment, entry and uncoating occur.

Avian influenza viruses can directly infect humans. In addition research into animal viruses has made an important contribution to our understanding of viruses in general, their replication, molecular biology, evolution, and interaction with the host.

Rhabdoviruses are a diverse family of single stranded, negative sense RNA viruses that can successfully utilize a myriad of ecological niches, ranging from plants and insects, to fish and mammals. This virus family includes pathogens such as rabies virus, vesicular stomatitis virus, and potato yellow dwarf virus that are of tremendous public health, veterinary, and agricultural significance.

Due to the relative simplicity of their genomes and morphology, in recent years rhabdoviruses have become powerful model systems for studying molecular virology. This picornavirus is the etiological agent of an acute systemic vesicular disease that affects cattle worldwide, foot-and-mouth disease. FMDV is a highly variable and transmissible virus. It enters the body through inhalation. Soon after infection, the single stranded positive RNA that constitutes the viral genome is efficiently translated using a cap-independent mechanism driven by the internal ribosome entry site element IRES.

This process occurs concomitantly with the inhibition of cellular protein synthesis, caused by the expression of viral proteases. In depth knowledge of the molecular basis of the viral cycle is needed to control viral pathogenesis and disease spreading. The molecular biology of pestiviruses shares many similarities and peculiarities with the human hepaciviruses.

Genome organization and translation strategy are highly similar for the members of both genera. One hallmark of pestiviruses is their unique strategy to establish persistent infection during pregnancy. Coronavirus CoV genome replication takes place in the cytoplasm in a membrane-protected microenvironment, and starts with the translation of the genome to produce the viral replicase.

Vaccines traditionally consist of an attenuated weakened or killed version of the virus, although many vaccines now target specific immunogenic targets unique to a particular pathogen. Both viral and cellular proteins are required for replication and transcription. CoVs initiate translation by cap-dependent and cap-independent mechanisms.

Cell macromolecular synthesis may be controlled after CoV infection by locating some virus proteins in the host cell nucleus. Infection by different coronaviruses cause in the host alteration in the transcription and translation patterns, in the cell cycle, the cytoskeleton, apoptosis and coagulation pathways, inflammation, and immune and stress responses.

The balance between genes up- and down-regulated could explain the pathogenesis caused by these viruses. Antiviral drugs are a class of medication used specifically for treating viral infections. Like antibiotics for bacteria, antiviral drugs are usually specific for a particular virus.

Unlike most antibiotics, antiviral drugs do not destroy their target pathogen; instead they inhibit their development. In addition to targeting viral infections directly, some therapeutics work by enhancing the immune responses necessary for viral clearance. One of the best-known of this class of drugs are interferons, which inhibit viral synthesis in infected cells. Interferons IFNs play pivotal roles in shaping the immune responses in mammals and are particularly important for the control of viral infections, cell growth, and immune regulation.

In order to survive, viruses have evolved multiple strategies to evade the anti-viral effects of IFNs. Elucidating the molecular and cellular biology of the virus-interferon interaction is key to understanding issues such as viral pathogenesis, latency, and the development of novel antivirals. Pediatric polio vaccination in India by a Stop Transmission of Polio STOP teams : Vaccinations are the best defense against a wide range of viruses, but they are not effective in treating active infections.

Privacy Policy. Skip to main content. Search for:. DNA Viruses in Eukaryotes. Like most viruses, the genomes of most single stranded DNA viruses are small, encoding only a few proteins, and are therefore dependent on host cell factors for replication.

Double stranded DNA viruses only infect lower species of plants, such as algae. These viruses are huge dsDNA viruses with genomes ranging from to kb with up to protein-encoding genes, making them distinctly different from viruses infecting higher plants. Plant viruses are generally spread through vectors, such as insects, but can also be passed from generation to generation.

Key Terms Baltimore Classification System : The Baltimore classification, developed by David Baltimore, is a virus classification system that groups viruses into families, depending on their type of genome DNA, RNA, single-stranded ss , double-stranded ds , etc. Key Takeaways Key Points From the perspective of the virus, the purpose of viral replication is to allow production and survival of its kind.

Most double-stranded DNA viruses replicate within the host cell nucleus, including polyomaviruses, adenoviruses, and herpesviruses—poxviruses, however, replicate in the cytoplasm. Adenoviruses and herpes viruses encode their own replication factors. Double-Stranded DNA Viruses: Herpesviruses Herpes viruses cause a wide range of latent, recurring infections including oral and genital herpes, cytomegalovirus, and chicken pox. Learning Objectives Recognize the attributes of herpes viruses.

The structure of herpes viruses consists of a relatively large double-stranded, linear DNA genome encased within an icosahedral protein cage called the capsid, which is wrapped in a lipid bilayer called the envelope. There is no method to eradicate herpes virus from the body, but antiviral medications, such as acyclovir, can reduce the frequency, duration, and severity of outbreaks. Key Terms tegument : A natural covering of the body or of a bodily organ.

Reactivation of latent viruses This has been implicated in a number of diseases e. First, complementary viral and cell surface receptors bring the viral and host cell membranes into close proximity. Next, the two membranes begin to merge, forming a hemifusion state. Key Terms glycoprotein : A protein with covalently bonded carbohydrates. Replication of Herpes Simplex Virus Herpes replication entails three phases: gene transcription, viral assembly in the nucleus, and budding through the nuclear membrane.

Learning Objectives Review the herpes simplex viral replication cycle. Key Takeaways Key Points Upon entry into the host cell nucleus, three distinct phases of gene transcription and protein synthesis are initiated, producing the immediate-early, early, and late proteins. Viral nucleocapsid assembly occurs within the host cell nucleus.

Key Terms nucleocapsid : The core structure of a virus, consisting of nucleic acid surrounded by a coat of protein. Immunodeficiency Immunodeficiency occurs when the immune system cannot appropriately respond to infections.

Learning Objectives Explain the problems associated with immunodeficiency. Key Takeaways Key Points If a pathogen is allowed to proliferate to certain levels, the immune system can become overwhelmed; immunodeficiency occurs when the immune system fails to respond sufficiently to a pathogen. Immunodeficiency can be caused by many factors, including certain pathogens, malnutrition, chemical exposure, radiation exposure, or even extreme stress. HIV is a virus that causes immunodeficiency by infecting helper T cells, causing cytotoxic T cells to destroy them.

Learning Objectives Examine pox viruses for their relevance to human disease and research. Key Takeaways Key Points The most famous of the poxviruses was smallpox. The most abundant and simplest infectious form of the poxvirus particle, the mature virion, consists of the viral DNA genome encased in a proteinaceous core and an outer lipoprotein membrane.

Poxviruses exhibit a temporally-regulated gene expression program: early, intermediate, and late genes drive DNA replication followed by expression of structural proteins necessary for progeny virion assembly. Key Terms recombinant : This term refers to something formed by combining existing elements in a new combination. Learning Objectives Define the characteristics of adenoviruses. Adenoviruses bind cell surface receptors on host cells, resulting in entry of the virion into the host cell within an endosome.

Early genes are responsible for expressing mainly non-structural, regulatory proteins, while late genes produce structural protein necessary for viral replication. Key Terms endosome : An endocytic vacuole through which molecules are internalized during endocytosis pass, en route to lysosomes.

Learning Objectives Differentiate between retroviruses and hepadnaviruses. Key Terms endogenous : produced, originating or growing from within episome : A segment of DNA that can exist and replicate either autonomously in the cytoplasm or as part of achromosome, mainly found in bacteria. Treatment of Animal Viral Infections Interferons play pivotal roles in shaping the immune responses in mammals.