Gene regulation
Viral Suppressors of RNA Silencing
Mechanism of Action of Viral Suppressors of RNA Silencing
from József Burgyán writing in Recent Advances in Plant Virology
RNA silencing is an evolutionarily conserved sequence-specific gene-inactivation system that also functions as an antiviral mechanism in higher plants and insects. To overcome this defence system, viruses encode suppressors of RNA silencing, which can counteract the host silencing-based antiviral process. More than 50 individual viral suppressors have been identified from almost all plant virus genera, underlining their crucial role in successful virus infection. Viral suppressors are considered to be of recent evolution, and they are surprisingly diverse within and across kingdoms, exhibiting no obvious sequence similarity. Virus-encoded silencing suppressors can target several key components in the silencing machinery, such as silencing-related RNA structures and essential effector proteins and complexes. There has been much recent progress in our understanding of the mechanism and function of viral suppressors of antiviral RNA silencing in plants.
Further reading: Recent Advances in Plant Virology | Virology Publications | RNA and the Regulation of Gene Expression
from József Burgyán writing in Recent Advances in Plant Virology
RNA silencing is an evolutionarily conserved sequence-specific gene-inactivation system that also functions as an antiviral mechanism in higher plants and insects. To overcome this defence system, viruses encode suppressors of RNA silencing, which can counteract the host silencing-based antiviral process. More than 50 individual viral suppressors have been identified from almost all plant virus genera, underlining their crucial role in successful virus infection. Viral suppressors are considered to be of recent evolution, and they are surprisingly diverse within and across kingdoms, exhibiting no obvious sequence similarity. Virus-encoded silencing suppressors can target several key components in the silencing machinery, such as silencing-related RNA structures and essential effector proteins and complexes. There has been much recent progress in our understanding of the mechanism and function of viral suppressors of antiviral RNA silencing in plants.
Further reading: Recent Advances in Plant Virology | Virology Publications | RNA and the Regulation of Gene Expression
miRNAs in Mammalian Antiviral Immune Responses
Virus-encoded Suppressors of RNA Silencing and the Role of Cellular miRNAs in Mammalian Antiviral Immune Responses
from Joost Haasnoot and Ben Berkhout writing in RNA Interference and Viruses
Small RNA-directed silencing mechanisms play important roles in the regulation of eukaryotic gene expression. In plants, insects, nematodes and fungi RNA silencing mechanisms are also involved in innate antiviral defence responses. To counter antiviral RNA silencing, viruses from plants, insects and fungi encode RNA silencing suppressors (RSSs). Recent studies suggest that RNA silencing in mammals, or RNA interference (RNAi), is also involved in antiviral responses. In particular, there is increasing evidence that cellular regulatory microRNAs (miRNAs) have a function in restricting virus replication in mammalian cells. Similar to plant and insect viruses, several mammalian viruses encode RSS factors that inhibit the RNAi mechanism. Several of these suppressors are multifunctional proteins that were previously shown to block innate antiviral immune responses involving the interferon (IFN) pathway.
Further reading: Recent Advances in Plant Virology | RNA Interference and Viruses | RNA and the Regulation of Gene Expression
from Joost Haasnoot and Ben Berkhout writing in RNA Interference and Viruses
Small RNA-directed silencing mechanisms play important roles in the regulation of eukaryotic gene expression. In plants, insects, nematodes and fungi RNA silencing mechanisms are also involved in innate antiviral defence responses. To counter antiviral RNA silencing, viruses from plants, insects and fungi encode RNA silencing suppressors (RSSs). Recent studies suggest that RNA silencing in mammals, or RNA interference (RNAi), is also involved in antiviral responses. In particular, there is increasing evidence that cellular regulatory microRNAs (miRNAs) have a function in restricting virus replication in mammalian cells. Similar to plant and insect viruses, several mammalian viruses encode RSS factors that inhibit the RNAi mechanism. Several of these suppressors are multifunctional proteins that were previously shown to block innate antiviral immune responses involving the interferon (IFN) pathway.
Further reading: Recent Advances in Plant Virology | RNA Interference and Viruses | RNA and the Regulation of Gene Expression
RNA Silencing and the Interplay Between Plants and Viruses
RNA Silencing and the Interplay Between Plants and Viruses
from Lourdes Fernández-Calvino, Livia Donaire and César Llave writing in Recent Advances in Plant Virology
In eukaryotes, RNA silencing controls gene expression to regulate development, genome stability and stress-induced responses. In plants, this process is also recognized as a major immune system targeted against plant viruses. Plant viruses stimulate RNA silencing responses though formation of viral RNA with double-stranded features that are subsequently processed into functional small RNAs (sRNAs). Recent studies highlight the complexity of the viral sRNA populations and their potential to associate with multiple silencing effector complexes. This fact has profound implications in the cross-talk interactions between plants and viruses since both virus genomes and host genes are putative targets of viral sRNAs. The concept of RNA silencing is an elegant natural antiviral mechanism in plants. Viral sRNA-mediated regulation of gene expression is important in the frame of compatible interactions between plants and viruses.
Further reading: Recent Advances in Plant Virology | Virology Publications | RNA and the Regulation of Gene Expression
from Lourdes Fernández-Calvino, Livia Donaire and César Llave writing in Recent Advances in Plant Virology
In eukaryotes, RNA silencing controls gene expression to regulate development, genome stability and stress-induced responses. In plants, this process is also recognized as a major immune system targeted against plant viruses. Plant viruses stimulate RNA silencing responses though formation of viral RNA with double-stranded features that are subsequently processed into functional small RNAs (sRNAs). Recent studies highlight the complexity of the viral sRNA populations and their potential to associate with multiple silencing effector complexes. This fact has profound implications in the cross-talk interactions between plants and viruses since both virus genomes and host genes are putative targets of viral sRNAs. The concept of RNA silencing is an elegant natural antiviral mechanism in plants. Viral sRNA-mediated regulation of gene expression is important in the frame of compatible interactions between plants and viruses.
Further reading: Recent Advances in Plant Virology | Virology Publications | RNA and the Regulation of Gene Expression
Bacterial Histone-Like HU Proteins
Bacterial histone-like HU proteins are critical to maintenance of the nucleoid structure. In addition, they participate in all DNA-dependent functions, including replication, repair, recombination and gene regulation. Their function is typically architectural, inducing a specific DNA topology that promotes assembly of higher-order nucleo-protein structures.
Although HU proteins are highly conserved, individual homologs have been shown to exhibit a wide range of different DNA binding specificities and affinities. The existence of such distinct specificities indicates functional evolution and predicts distinct in vivo roles. Emerging evidence suggests that HU proteins discriminate between DNA target sites based on intrinsic flexure, and that two primary features of protein binding contribute to target site selection: The extent to which protein-mediated DNA kinks are stabilized and a network of surface salt-bridges that modulate interaction between DNA flanking the kinks and the body of the protein.
These features confer target site selection for a specific HU homolog, they suggest the ability of HU to induce different DNA structural deformations depending on substrate, and they explain the distinct binding properties characteristic of HU homologs. Further divergence is evidenced by the existence of HU homologs with an additional lysine-rich domain also found in eukaryotic histone H1.
Further reading: Functional Evolution of Bacterial Histone-Like HU Proteins
Although HU proteins are highly conserved, individual homologs have been shown to exhibit a wide range of different DNA binding specificities and affinities. The existence of such distinct specificities indicates functional evolution and predicts distinct in vivo roles. Emerging evidence suggests that HU proteins discriminate between DNA target sites based on intrinsic flexure, and that two primary features of protein binding contribute to target site selection: The extent to which protein-mediated DNA kinks are stabilized and a network of surface salt-bridges that modulate interaction between DNA flanking the kinks and the body of the protein.
These features confer target site selection for a specific HU homolog, they suggest the ability of HU to induce different DNA structural deformations depending on substrate, and they explain the distinct binding properties characteristic of HU homologs. Further divergence is evidenced by the existence of HU homologs with an additional lysine-rich domain also found in eukaryotic histone H1.
Further reading: Functional Evolution of Bacterial Histone-Like HU Proteins
MicroRNAs as Regulators of Host-virus Interactions
from Sassan Asgari and Christopher S. Sullivan in Insect Virology
MicroRNAs (miRNAs) are small non-coding RNA molecules that play a central role in the regulation of gene expression impacting many biological processes. These include development, cancer, apoptosis, immunity, and longevity. In addition, accumulating evidence suggest that miRNAs are likely to be involved in host-virus interactions by modulating expression levels of either defence genes or virus genes. Several groups of animal viruses, as well as insect viruses, encode miRNAs that are instrumental in virus biology, including replication, pathogenesis and latency. Of interest is the biogenesis of miRNAs, current approaches to the discovery of miRNAs, their mode of action and strategies for determining viral miRNA function.
Further reading: Insect Virology
MicroRNAs (miRNAs) are small non-coding RNA molecules that play a central role in the regulation of gene expression impacting many biological processes. These include development, cancer, apoptosis, immunity, and longevity. In addition, accumulating evidence suggest that miRNAs are likely to be involved in host-virus interactions by modulating expression levels of either defence genes or virus genes. Several groups of animal viruses, as well as insect viruses, encode miRNAs that are instrumental in virus biology, including replication, pathogenesis and latency. Of interest is the biogenesis of miRNAs, current approaches to the discovery of miRNAs, their mode of action and strategies for determining viral miRNA function.
Further reading: Insect Virology