Plant RNA Viruses
Replication of Plant RNA Viruses
from Peter D. Nagy and Judit Pogany writing in Recent Advances in Plant Virology
Among plant viruses, the positive-stranded RNA [(+)RNA] viruses are the largest group, and the most widespread. The central step in the infection cycle of (+)RNA viruses is RNA replication, which is carried out by virus-specific replicase complexes consisting of viral RNA-dependent RNA polymerase, one or more auxiliary viral replication proteins, and a number of co-opted host factors. Viral replicase complexes assemble in specialized membranous compartments in infected cells. Sequestering the replicase complexes is not only helpful for rapid production of a large number of viral (+)RNA progeny, but it also facilitates avoiding recognition by the host¹s anti-viral surveillance system, and it provides protection from degradation of the viral RNA. Successful viral replication is followed by cell-to-cell and long-distance movement throughout the plant, as well as encapsidation of the (+)RNA progeny to facilitate transmission to new plants. A recent review provides an overview of our current understanding of the molecular mechanisms in plant (+)RNA virus replication. Recent significant progress in this research area is based on development of powerful in vivo and in vitro methods, including replicase assays, reverse genetic approaches, intracellular localization studies, genome-wide screens for co-opted host factors and the use of plant or yeast model hosts.
Further reading: Recent Advances in Plant Virology | Virology Publications | RNA and the Regulation of Gene Expression
from Peter D. Nagy and Judit Pogany writing in Recent Advances in Plant Virology
Among plant viruses, the positive-stranded RNA [(+)RNA] viruses are the largest group, and the most widespread. The central step in the infection cycle of (+)RNA viruses is RNA replication, which is carried out by virus-specific replicase complexes consisting of viral RNA-dependent RNA polymerase, one or more auxiliary viral replication proteins, and a number of co-opted host factors. Viral replicase complexes assemble in specialized membranous compartments in infected cells. Sequestering the replicase complexes is not only helpful for rapid production of a large number of viral (+)RNA progeny, but it also facilitates avoiding recognition by the host¹s anti-viral surveillance system, and it provides protection from degradation of the viral RNA. Successful viral replication is followed by cell-to-cell and long-distance movement throughout the plant, as well as encapsidation of the (+)RNA progeny to facilitate transmission to new plants. A recent review provides an overview of our current understanding of the molecular mechanisms in plant (+)RNA virus replication. Recent significant progress in this research area is based on development of powerful in vivo and in vitro methods, including replicase assays, reverse genetic approaches, intracellular localization studies, genome-wide screens for co-opted host factors and the use of plant or yeast model hosts.
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