The iridoviruses generate cytoplasmic factories and crystalline arrays

Iridoviruses Iridoviruses are large dsDNA viruses with genomes ranging from 100 to 210 kbp in length encoding between 100 and 230 proteins (Williams et al., 2005). Much of the work on iridovirus replication has been carried out on the ranavirus frog virus 3 (FV3). FV3 genome synthesis occurs in the nucleus and cytoplasm. No nuclear inclusions have been reported during FV3 infection, and as such it is unclear how the nuclear replication stage is mediated. However, viral DNA is initially...

Cytoplasmic inclusions form during late stages of herpesvirus tegumentation The cytoplasmic assembly compartment

The tegument layer of alphaherpesviruses is composed of at least 15 different proteins (Mettenleiter, 2002). US11, UL17, UL47, UL48, and UL49 are components of the tegument, and all are localized to the nucleus (if not exclusively) during the productive life cycle of the virus (Fuchs et al., 2002 Hutchinson et al., 2002 Kopp et al., 2002 Roller and Roizman, 1992 Taus et al., 1998). UL48 may play a role in egress from the nucleus, though this has not been unequivocally established (Mossman et...

Causal relationship between a virus and a disease

One of the biggest challenges of studying virus pathogenesis in honey bees is linking the virus infection with a particular disease and therefore evaluating the economic impact of the virus infection. In the field, honey bees are often infected by multiple viruses simultaneously, most of these viruses usually persisting as latent infections in the bee hosts. In addition, virus infections in honey bees are often associated with the infection of other pathogens and infestation of parasites....

Tissue tropism

The ability of a virus to invade the tissues of a host is a fundamental requirement for a successful infection. The term ''tissue tropism'' is referred to as the specificity of a virus to infect and replicate in particular cells or tissues. Tissue tropism is determined mostly by (1) the chemical affinity of the virus attachment protein with virus-specific receptors on the surface of a host cell (2) the suitability of viral entry sites to support virus replication and (3) the ability of the...

Virus Nomenclature And Classification

For several years I was actively involved in virus nomenclature and classification (Maramorosch, 1974). My interest stemmed from the finding that several leafhopper-borne viruses that were inducing plant diseases were multiplying not only in plants but also in their invertebrate animal vectors. The finding that little or no harm was observed in the virus-carrying insects could suggest that these viruses originated as insect viruses and over long periods of evolution became harmless to their...

Nuclear inclusions formed during polyomavirus and papillomavirus infection

Polyoma- and papillomaviruses are small double-stranded tumorigenic DNA viruses with genomes of 5 and 8 kbp, respectively. Replication and assembly of these two viruses follow similar strategies, and both involve ND10 bodies. The VP1 capsid protein of human polyomavirus JC is targeted to ND10 domains by VP2, VP3, and agnoprotein where they are assembled into virions (Shishido-Hara et al., 2004). A similar process occurs during papillomavirus infection where the minor capsid protein, L2, is...

Vesicle coat proteins may play a role during picornavirus replication

Evidence that different members of the picornavirus family vary in the way that they interact with host membranes is provided by studies of virus sensitivity to BFA. BFA completely inhibits Poliovirus and echovirus 11 replication (Cuconati et al., 1998 Gazina et al., 2002 Irurzun et al., 1992 Maynell et al., 1992) and partially inhibits parechovirus 1 replication (Gazina et al., 2002) but not other picornaviruses such as EMCV (Gazina et al., 2002) or FMDV (Monaghan et al., 2004 O'Donnell et...

Nuclear inclusions also form as sites of herpesvirus assembly The assemblon

A second prominent nuclear inclusion induced by herpesvirus infection is the assemblon (Ward et al., 1996b). This is the site where capsid proteins accumulate and assemble into nucleocapsids (Fig. 8B). The assembly of herpesvirus nucleocapsids has been researched in great detail at the ultrastructural level facilitated by a cell-free system for reconstituting the particles (Heymann et al., 2003 Newcomb et al., 1994,1996). The mature herpesvirus capsid is icosahedral with a T 16 symmetry and is...

Flavivirus nonstructural proteins can induce membrane rearrangements

Studies have investigated which viral proteins are responsible for membrane rearrangements seen in cells infected with flaviviruses. The NS4A of Kunjin virus induces the characteristic convoluted membranes and paracrystalline arrays seen in flavivirus infections. The NS4A-B protein also causes membrane rearrangement, but the highly condensed structures seen in infected cells are not produced until the NS2B-3 protease cleaves NS4A free from NS4B Roosendaal et al., 2006 . The NS4B then...

The picornavirus replicase

Picornaviruses are nonenveloped positive-stranded RNA viruses. The genome encodes a large polyprotein that is processed to generate capsid proteins from the P1 region and nonstructural replicase proteins from the P2 and P3 regions. Picornavirus 3D contains the RdRp, while 2C has NTPase and helicase motifs. The 3D polymerase does not have membrane-targeting information but is synthesized as a 3ABCD precursor. 3ABCD is processed to 3AB by the 3C protease, and a hydrophobic domain in 3A targets...

Membrane rearrangements may vary between different picornavirus families

Gazina et al. 2002 have studied replication complexes formed by several different picornaviruses. Encephalomyocarditis virus EMCV , parecho-virus 1, and echovirus 11 induce clustered vesicles containing dsRNA in the perinuclear region of the cell. The precise nature of the vesicles varied with virus. Parechovirus 1 produced homogeneous vesicles of 70-100 nm, while membranes produced by EMCV and echovirus 11 were heterogeneous but more compact and associated with electron-dense material....

Picornavirus replication blocks protein secretion

Poliovirus and coxsackievirus slow protein movement through the secretory pathway Doedens and Kirkegaard, 1995 Wessels et al., 2005 . Expression of 2B, 2BC, and 3A individually were all able to slow secretion Cornell et al., 2006 Doedens and Kirkegaard, 1995 Doedens et al., 1997 van Kuppeveld et al., 1997 Wessels et al., 2005,2006a , but for both viruses the 3A protein was found to have the greatest impact on ER-to-Golgi transport. Poliovirus infection, and the 3A protein expressed alone in...

Transmission Modes

Viruses are obligate intracellular parasites that can only multiply inside living host cells utilizing the host cell's metabolic machinery. In order to survive, viruses must have ways to invade hosts and be transmitted from one host to another. Transmission processes determine the persistence and the spread of viruses in a population. In theory, transmission of a virus can occur horizontally or vertically, or both. In horizontal transmission, viruses are transmitted between different...

Coxsackievirus replication

The formation of COPI-coated vesicles is regulated by the Arf1-GTPase. The observation that BFA inhibits the replication of enteroviruses such as Poliovirus, and also inhibits the function of the Arf1-GTPase, provides a second link between virus replication and COPI coats. Arf proteins are regulated by Arf-GEFs that facilitate binding of GTP by removing GDP, and by Arf-GAPs that increase hydrolysis of GTP by Arfs. Arf1-GEFs are inhibited by BFA, and BFA therefore reduces levels of Arf1-GTP in...

Viroplasm Virosomes Factories And Inclusions

Virus replication sites have been studied for many years and have evolved their own terminology. Early studies of poxvirus replication Dales and Siminovitch, 1961 Morgan et al., 1954 describe electron-dense aggregates and amorphous material induced early during infection called viroplasm. Viroplasm has also been used to describe similar structures induced during infection with Poliovirus Dales et al., 1965a . Viroplasm is often concentrated within perinuclear areas that exclude host organelles....

Poxviruses generate virus factories and inclusions

Viroplasm Guarnieri Bodies

Poxviruses are large dsDNA viruses with genomes ranging from 130 to 375 kbp. Poxvirus gene expression follows the regulated cascade of other large dsDNA viruses with early, intermediate, and late transcripts described. Poxvirus progeny genomes are replicated exclusively in the cytoplasm in virus factories. The virus encodes all the enzymes necessary for transcription and replication of its genome. Genetic analysis has identified a minimum of five viral genes necessary for genome replication,...

Brooklyn Botanic Garden

My luck continued when I was hired as technician at the Brooklyn Botanic Garden. My boss and first mentor was Dr. Lindsay M. Black Fig. 1 , who had moved from the Rockefeller Institute Branch in Princeton to the Botanic Garden a year earlier. He hired me to assist in his studies of plant viruses transmitted by leafhopper vectors. I learned how to maintain leafhopper colonies and how to transfer individual leafhoppers to test plants. Catching the tiny insects and placing them on caged plants...