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At least 181 records · Page 10Linked to original sources
PubMed1990

Myristoylation of gag proteins of HIV-1 plays an important role in virus assembly.

The gag proteins of HIV-1 are modified by the addition of myristic acid to the amino terminal glycine residue. Site-directed mutagenesis was used to construct a mutant of HIV-1 in which this glycine residue was changed to an alanine. Upon transfection into cos-1 cells, the mutant genome directed the synthesis of the full complement of HIV-1 proteins, but p17 and p17-containing polyproteins were not myristoylated. The cells transfected with the mutant DNA did not release any virus particles and no viral cores were visible by electron microscopy. Furthermore, supernatant from these transfected cells failed to infect CEM cells. The expression and function of gp120 on the surface of cells transfected with the mutant DNA was unaffected as these cells formed syncytia comparable in both size and number to the ones obtained with wild-type DNA.

Amino Acid Sequence↗
PubMed1977

Configuration of tobacco mosaic virus, RNA during virus assembly.

When TMV reassembles, the uncoated RNA is folded back along the growing rod, probably down the central hole. This surprising configuration is essential for rapid elongation--presumably supplying RNA to its site of incorporation while keeping the bulk of the free RNA out of the way.

Kinetics↗
PubMed1978

Role of the host in virus assembly: cloning of the Escherichia coli groE gene and identification of its protein product.

Correct assembly of the heads of bacteriophages lambda and T4 requires the function of the groE gene of the Escherichia coli host. We have isolated a transducing derivative of lambda, called lambda gt-Ec.groE, that carries a functional copy of the groE gene. Unlike wild-type lambda, this phage is able to form plaques on hosts with a mutant groE gene. We have isolated an amber mutation in the groE gene carried by the phage, and this has made it possible to identify the groE product as a protein of molecular weight 65,000. In the phage, the groE gene is under the control of an early phage promoter.

Bacterial Proteins↗
PubMed1987

Cloning and expression of the filamentous bacteriophage Pf1 major coat protein gene in Escherichia coli. Membrane protein processing and virus assembly.

A restriction fragment carrying the major coat protein gene (gene VIII) was excised from the replicative form (RF) DNA of the class II filamentous bacteriophage Pf1, which infects Pseudomonas aeruginosa. This fragment was cloned into the expression plasmid pKK223-3, where it came under the control of the tac promoter. In transformed Escherichia coli JM101 cells, in the presence of the inducer isopropyl-beta-D-thiogalactoside, the bacteriophage Pf1 gene was strongly expressed. The bacteriophage Pf1 coat protein displays the same pattern of negatively charged N-terminal region, hydrophobic middle region and positively charged C-terminal region as that of its counterpart in the class I bacteriophage fd, which infects E. coli, but otherwise the two proteins have no sequence homology. However, the Pf1 procoat protein was found to undergo processing and insertion into the E. coli cell inner membrane, like its fd counterpart, demonstrating that this part of the assembly process is the same for these different bacteriophages. The complete transcriptional unit, incorporating the tac promoter and rrnB transcription terminators flanking the Pf1 coat protein gene, was excised from the expression plasmid and cloned into the intergenic space of bacteriophage R252, an fd bacteriophage that carries an amber mutation in its own major coat protein gene. The Pf1 coat protein gene was again well expressed in infected E. coli cells but the chimeric bacteriophage had growth properties identical to those of the parent bacteriophage R252 on suppressor and non-suppressor strains of E. coli. The class I bacteriophage Pf1 coat protein evidently cannot be recognized by the class I bacteriophage assembly complex at or in the E. coli cell inner membrane, either at the point of initiation of assembly or during the elongation process.

Amino Acid Sequence↗
PubMed1993

Bacillus subtilis mutants defective in bacteriophage phi 29 head assembly.

Virus assembly mutants of asporogenous Bacillus subtilis defective in bacteriophage phi 29 head assembly were detected by the use of antibodies that reacted strongly with the free dodecameric phi 29 portal vertex composed of gene product 10 (gp10) but weakly with the portal vertex assembled into proheads or phage. Phage adsorption and the synthesis of phage proteins, DNA-gene product 3, and prohead RNA were normal in these mutants, but prohead and phage production was greatly reduced. The assembly defect was transferred to competent B. subtilis by transformation and transduction. PBS1 transduction showed that the vam locus was linked to Tn917 located at 317 degrees on the B. subtilis chromosome.

Bacillus Phages↗
PubMed1997

Mutations in the matrix protein of human immunodeficiency virus type 1 inhibit surface expression and virion incorporation of viral envelope glycoproteins in CD4+ T lymphocytes.

Highly conserved amino acids in the second helix structure of the human immunodeficiency virus type 1 (HIV-1) MA protein were identified to be critical for the incorporation of viral Env proteins into HIV-1 virions from transfected COS-7 cells. The effects of these MA mutations on viral replication in the HIV-1 natural target cells, CD4+ T lymphocytes, were evaluated by using a newly developed system. In CD4+ T lymphocytes, mutations in the MA domain of HIV-1 Gag also inhibited the incorporation of viral Env proteins into mature HIV-1 virions. Furthermore, mutations in the MA domain of HIV-1 Gag reduced surface expression of viral Env proteins in CD4+ T lymphocytes. The synthesis of gp160 and cleavage of gp160 to gp120 were not significantly affected by MA mutations. On the other hand, the stability of gp120 in MA mutant-infected cells was significantly reduced compared to that in the parental wild-type virus-infected cells. These results suggest that functional interaction between HIV-1 Gag and Env proteins is not only critical for efficient incorporation of Env proteins into mature virions but also important for proper intracellular transport and stable surface expression of viral Env proteins in infected CD4+ T lymphocytes. A single amino acid substitution in MA abolished virus infectivity in dividing CD4+ T lymphocytes without significantly affecting virus assembly, virus release, or incorporation of Gag-Pol and Env proteins, suggesting that in addition to its functional role in virus assembly, the MA protein of HIV-1 also plays an important role in other steps of virus replication.

Amino Acid Sequence↗
PubMed1980

Structural studies of the assembly of simple viruses.

The principles of structural design and the bonding properties of structural proteins form a basis for the study of virus assembly. Virus coat proteins are designed specifically to interact with one another and with the viral nucleic acid to form a stable virus particle. The process of assembly is controlled by the switching of protein subunit conformation, which can alter the binding properties of the subunits. The self-assembly processes of several simple viruses in vitro have significantly different rates of assembly and specificities for their viral nucleic acid. It is possible that many viruses have multiple pathways for assembly, each pathway exhibiting somewhat different characteristics but all resulting in identical infectious virus particles.

Bacteriophages↗
PubMed1980

RNA-protein interactions in the assembly of tobacco mosaic virus.

Assembly of tobacco mosaic virus is initiated by the binding of a specific loop of the RNA into the central hole of the disk aggregate of protein subunits. Since the nucleation loop is located about five-sixths along the RNA molecule, subsequent elongation must be bidirectional. We have now measured the rates of elongation in the two directions by determining the lengths of RNA protected from nuclease digestion at different times and using either intact TMV rNA, or RNA with most of the longer tail removed. Comparison of the rates with the protein supplied as either a mixture of disks with A-protein (a mixture of less aggregated states) or just A-protein, shows that different mechanisms and protein aggregates are used for the most rapid growth. When disks are present, they add more rapidly along the longer RNA tail but do not appear to add directly on the shorter tail. In contrast, smaller aggregates (A-protein) can add at both ends of the rod, but do so more slowly. Mechanisms for these processes are discussed. Preliminary results on the binding of the specific hexanucleotide AAGAAG to the disk are given and compared with the known changes on binding nonspecific hexanucleotides or the trinucleotide AAG.

Kinetics↗
PubMed1995

Point mutations in the coat protein of cucumber mosaic virus affect symptom expression and virion accumulation in tobacco.

We examined the correlation of the amino acid at position 129 in the coat protein (CP) of cucumber mosaic virus (CMV) with the phenotype of the viral pathology in tobacco by using CP mutants in which several amino acid substitutions had been introduced. An exchange between Ser129 in CMV-Y, a chlorosis-inducing strain, and Pro129 of CMV-O, a green-mosaic-inducing strain, reciprocally altered the phenotypes of those virus strains on tobacco. Replacement of either Ser129 in CMV-Y or Pro129 in CMV-O with a Leu, as is found in a chlorosis-inducing strain, CMV-M, resulted in veinal necrosis. Furthermore, we created mutants that have a Phe or a Gly at position 129. Two Phe129 mutants induced necrotic lesions on the inoculated leaves, and a Gly129 mutant induced green mosaic symptoms. In inoculated protoplasts, the mutant viruses and the wild-type virus all replicated RNA well, and accumulated CP; however, infection with the Leu129 and Phe129 mutants yielded few virions. The Phe129 mutants lacked the capacity to move systemically in tobacco; by 2 weeks post-inoculation, the Phe129 mutants occasionally gave rise to revertants that elicited chlorosis, green mosaic or veinal necrosis. Sequence analysis revealed that one had reverted to the parental Y strain, and the others had additional single amino acid changes (positions 138, 144 or 147). We suggest that amino acids at specific sites affect the whole structure of the CP and affect virus assembly, virus transport and symptom expression.

Amino Acid Sequence↗