Factors Determining the Site of Synthesis of Polio Virus Proteins: The Early Attachment of Virus Particles to Endoplasmic Membranes

1973 ◽  
Vol 13 (2) ◽  
pp. 403-413
Author(s):  
M. L. FENWICK ◽  
MARGARET J. WALL
Keyword(s):  
Protein Synthesis ◽  
Early Stage ◽  
Cellular Protein ◽  
Membrane Association ◽  
Viral Protein Synthesis ◽  
Polio Virus ◽  
Virus Particles ◽  
Sharp Band ◽  
Membrane Bound ◽  
Infectious Cycle

Cytoplasmic extracts of HeLa cells made 1 to 2 h after infection with radioactive poliovirus contained 150-S virus particles and 130-S, perhaps partially disrupted, particles. The latter were resistant to RNase but sensitive to dodecylsulphate. Both particles were associated with fast sedimenting material from which they could be released by deoxycholate, but not by EDTA. In isopycnic gradients of sucrose in D2O the labelled particles formed a sharp band coincident with membrane-bound ribosomes at a density of 1.23 g cm-3. It is suggested that attachment of virus particles to endoplasmic reticulum may be an early stage in the infectious cycle, determining the site of subsequent steps. The inhibition of cellular protein synthesis that develops during infection affects membrane-bound as well as free polysomes and therefore does not determine the membrane-association of viral protein synthesis.

Evidence that Sindbis virus infects BHK-21 cells via a lysosomal route

1980 ◽  
Vol 58 (10) ◽  
pp. 1131-1137 ◽  
Author(s):  
Pierre J. Talbot ◽  
Dennis E. Vance
Keyword(s):  
Protein Synthesis ◽  
Virus Infection ◽  
Sindbis Virus ◽  
Cellular Protein ◽  
Additive Effects ◽  
Lysosomal Function ◽  
Virus Particles ◽  
Lysosomal Ph ◽  
Weak Bases ◽  
Cellular Protein Synthesis

Chloroquine and NH4Cl, potent inhibitors of lysosomal function, decreased the production of infectious Sindbis virus particles in BHK-21 cells by 10- and 12-fold, respectively. There were no apparent toxic effects on cells exposed to these lysosomotropic agents. These chemicals did not alter the rate of cellular protein synthesis, with the exception of a reversible twofold inhibition by chloroquine. No additive effects of chloroquine and NH4Cl were observed when the cells were saturated with these weak bases, which suggests that their effect is exerted via the same mechanism, most likely as a result of an increase in lysosomal pH. The reduction in the formation of Sindbis virions was monitored by incorporation of [35S]methionine and shown to be fourfold by chloroquine or NH4Cl at 5 h postinfection but negligible at 11 h postinfection. These results strongly suggest that a productive Sindbis virus infection requires functional lysosomes. Thus, endocytosis is probably the main infectious mechanism for penetration of this virus into BHK-21 cells.

Exterior and Interior Events in Early Stage of Thrombin-induced Platelet Aggregation

1977 ◽  
Vol 38 (03) ◽  
pp. 0630-0639 ◽  
Author(s):  
Shuichi Hashimoto ◽  
Sachiko Shibata ◽  
Bonro Kobayashi
Keyword(s):  
Molecular Weight ◽  
Enzyme Activity ◽  
Plasma Membrane ◽  
Platelet Aggregation ◽  
Early Stage ◽  
Adenyl Cyclase ◽  
Cellular Component ◽  
Primary Event ◽  
Rabbit Platelets ◽  
Membrane Bound

SummaryTreatment of washed rabbit platelets with 1 u/ml of thrombin at 37° C resulted in a disappearance from platelets of a protein with 250,000 dalton molecular weight which was shown to be originated from plasma membrane. Parallel loss of adenyl cyclase was noted, and both reactions were complete within 30 sec. From the patterns of disc electrophoretograms, the importance of quick suppression of thrombin action in demonstrating the primary event was stressed.Thrombin induced an apparent activation of membrane bound phosphodiesterase. This reaction was also complete within 30 sec. The cellular component which contained the enzyme activity was distinct from plasma membrane. Soluble phosphodiesterase was not influenced by thrombin at all.These reactions required intact platelet cells to react with thrombin, and no reaction was detected when subcellular preparations were treated with thrombin.Possibility of collaboration of changes in externally located synthetic enzyme with those in internally located degrading enzyme in the early phase of thrombin action on platelets was suggested.

The history of anabolic steroids and a review of clinical experience with anabolic steroids

1985 ◽  
Vol 110 (3_Suppla) ◽  
pp. S11-S18 ◽  
Author(s):  
H. Kopera
Keyword(s):  
Protein Synthesis ◽  
Protein Metabolism ◽  
Anabolic Steroids ◽  
Muscular Activity ◽  
Living Cells ◽  
Cellular Protein ◽  
Complex Compounds ◽  
The Body ◽  
Anabolic Effect ◽  
Vital Functions

Metabolism is the term employed to embrace the various physical and chemical processes occurring within the tissues upon which the growth and heat production of the body depend and from which the energy for muscular activity, for the maintenance of vital activity and for the maintenance of vital functions is derived (Best & Taylor 1950). The destructive processes by which complex substances are converted by living cells into more simple compounds are called catabolism. Anabolism denotes the constructive processes by which simple substances are converted by living cells into more complex compounds, especially into living matter. Catabolism and anabolism are part of all metabolic processes, the carbohydrate, fat and protein metabolism. The term anabolic refers only to substances that exert an anabolic effect on protein metabolism and are unlikely to cause adverse androgenic effects. They shift the equilibrium between protein synthesis and degradation in the body as a whole in the direction of synthesis, either by promoting protein synthesis or reducing its breakdown. The protein anabolic effect of anabolic steroids is not restricted to single organs but is the result of stimulated biosynthesis of cellular protein in the whole organism.

An adenovirus mutant unable to express VAI RNA displays different growth responses and sensitivity to interferon in various host cell lines

1986 ◽  
Vol 6 (12) ◽  
pp. 4493-4498
Author(s):  
J Kitajewski ◽  
R J Schneider ◽  
B Safer ◽  
T Shenk
Keyword(s):  
Protein Synthesis ◽  
Host Cell ◽  
Rna Polymerase Iii ◽  
Growth Responses ◽  
Kb Cells ◽  
Viral Protein Synthesis ◽  
Viral Mrnas ◽  
Translational Initiation ◽  
Cell Extracts ◽  
293 Cells

The VAI RNA of adenovirus is a small, RNA polymerase III-transcribed species required for the efficient translation of host cell and viral mRNAs late after infection. VAI RNA prevented activation of the interferon-induced P1/eIF-2 alpha kinase. In its absence the kinase was activated, eIF-2 alpha was phosphorylated, and translational initiation was inhibited. H5dl331 (dl331), a mutant which cannot express VAI RNA, grew poorly in 293 cells but generated wild-type yields in KB cells. The growth phenotype of the mutant appeared to correlate with the kinetics of kinase induction and activation. Active kinase appeared more rapidly in cell extracts prepared from infected 293 cells, in which dl331 grew poorly, than in extracts of KB cells, in which the mutant grew well. However, when kinase was induced in KB cells by interferon treatment and then activated subsequent to dl331 infection, viral protein synthesis was less severely inhibited than in interferon-treated 293 cells. Thus, activated kinase per se is insufficient to severely inhibit dl331 protein synthesis in KB cells.

scholarly journals Protein Kinase R Is Responsible for the Phosphorylation of eIF2α in Rotavirus Infection

2010 ◽  
Vol 84 (20) ◽  
pp. 10457-10466 ◽  
Author(s):  
Margarito Rojas ◽  
Carlos F. Arias ◽  
Susana López
Keyword(s):  
Protein Synthesis ◽  
Kinase Domain ◽  
Cell Protein ◽  
Protein Kinase R ◽  
Viral Protein Synthesis ◽  
Α Subunit ◽  
Rotavirus Infection ◽  
Eif2α Phosphorylation ◽  
Infected Cells ◽  
Interferon System

ABSTRACT The eukaryotic initiation translation factor 2 (eIF2) represents a key point in the regulation of protein synthesis. This factor delivers the initiator Met-tRNA to the ribosome, a process that is conserved in all eukaryotic cells. Many types of stress reduce global translation by triggering the phosphorylation of the α subunit of eIF2, which reduces the formation of the preinitiation translation complexes. Early during rotavirus infection, eIF2α becomes phosphorylated, and even under these conditions viral protein synthesis is not affected, while most of the cell protein synthesis is blocked. Here, we found that the kinase responsible for the phosphorylation of eIF2α in rotavirus-infected cells is PKR, since in mouse embryonic fibroblasts deficient in the kinase domain of PKR, or in MA104 cells where the expression of PKR was knocked down by RNA interference, eIF2α was not phosphorylated upon rotavirus infection. The viral component responsible for the activation of PKR seems to be viral double-stranded RNA, which is found in the cytoplasm of infected cells, outside viroplasms. Taken together, these results suggest that rotaviruses induce the PKR branch of the interferon system and have evolved a mechanism to translate its proteins, surpassing the block imposed by eIF2α phosphorylation.

scholarly journals Differences in size, structure and function of free and membrane-bound polyribosomes of rat liver. Evidence for a single class of membrane-bound polyribosomes

1977 ◽  
Vol 168 (1) ◽  
pp. 1-8 ◽  
Author(s):  
J C Ramsey ◽  
W J Steele
Keyword(s):  
Protein Synthesis ◽  
Rat Liver ◽  
Size Structure ◽  
Large Fraction ◽  
Liver Homogenate ◽  
Structure And Function ◽  
Structural And Functional Properties ◽  
Membrane Bound ◽  
And Function

Free loosely bound and tightly bound polyribosomes were separated from rat liver homogenate by salt extraction followed by differential centrifugation, and several of their structural and functional properties were compared to resolve the existence of loosely bound polyribosomes and verify the specificity of the separation. The free and loosely bound polyribosomes have similar sedimentation profiles and polyribosome contents, their subunit proteins have similar electrophoretic patterns and their products of protein synthesis in vitro show a close correspondence in size and amounts synthesized. In contrast, the tightly bound polyribosomes have different properties from those of the free and loosely bound polyribosomes; their average size is significantly smaller; their polyribosome content is higher; their 60 S-subunit proteins lack two components and contain four or more components not found elsewhere; their products of protein synthesis in vitro differ in size and amounts synthesized. These observations show that rat liver membranes entrap a large fraction of the free polyribosomes at low salt concentrations and that these polyribosomes are similar to those of the free-polyribosome fraction and are different from those of the tightly bound polyribosome fraction in size, structure and function.

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