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At least 163 records · Page 9Linked to original sources
PubMed1993

Sendai virus assembly: M protein binds to viral glycoproteins in transit through the secretory pathway.

We have examined the relative ability of Sendai virus M (matrix) protein to associate with membranes containing viral glycoproteins at three distinct stages of the exocytic pathway prior to cell surface appearance. By the use of selective low-temperature incubations or the ionophore monensin, the transport of newly synthesized viral glycoproteins was restricted to either the pre-Golgi intermediate compartment (by incubation at 15 degrees C), the medial Golgi (in the presence of monensin), or the trans-Golgi network (by incubation at 20 degrees C). All three of these treatments resulted in a marked accumulation of the M protein on perinuclear Golgi-like membranes which in each case directly reflected the distribution of the viral F protein. Subsequent redistribution of the F protein to the plasma membrane by removal of the low-temperature (20 degrees C) block resulted in a concomitant redistribution of the M protein, thus implying association of the two components during intracellular transit. The extent of M protein-glycoprotein association was further examined by cell fractionation studies performed under each of the three restrictive conditions. Following equilibrium sedimentation of membranes derived from monensin-treated cells, approximately 40% of the recovered M protein was found to cofractionate with membranes containing the viral glycoproteins. Also, by flotation analyses, a comparable subpopulation of M protein was found to be membrane associated whether viral glycoproteins were restricted to the trans-Golgi network, the medial Golgi, or the pre-Golgi intermediate compartment. Additionally, transient expression of M protein alone from cloned cDNA showed that neither membrane association nor Golgi localization occurs in the absence of Sendai virus glycoproteins.

Animals↗
PubMed1986

Stereo images of vesicular stomatitis virus assembly.

Viral assembly was studied by viewing platinum replicas of cytoplasmic and outer plasma membrane surfaces of baby hamster kidney cells infected with vesicular stomatitis virus. Replicas of the cytoplasmic surface of the basilar plasma membrane revealed nucleocapsids forming bullet-shaped tight helical coils. The apex of each viral nose cone was anchored to the membrane and was free of uncoiled nucleocapsid, whereas tortuous nucleocapsid was attached to the base of tightly coiled structures. Using immunoelectron microscopy, we identified the nucleocapsid (N) viral protein as a component of both the tight-coil and tortuous nucleocapsids, whereas the matrix (M) protein was found only on tortuous nucleocapsids. The M protein was not found on the membrane. Using immunoreagents specific for the viral glycoprotein (G protein), we found that the amount of G protein per virion varied. The G protein was consistently localized at the apex of viral buds, whereas the density of G protein on the shaft was equivalent to that in the surrounding membrane. These observations suggest that G-protein interaction with the nucleocapsid via its cytoplasmic domain may be necessary for the initiation of viral assembly. Once contact is established, nucleocapsid coiling proceeds with nose cone formation followed by formation of the helical cylinder. M protein may function to induce a nucleocapsid conformation favorable for coiling or may cross-link adjacent turns in the tight coil or both.

Animals↗
PubMed1994

Coordinate regulation of replication and virus assembly by the large envelope protein of an avian hepadnavirus.

We have used linker scanning and site-directed mutagenesis in an attempt to distinguish among the known functions of the duck hepatitis B virus large envelope protein, p36. We found that linker-encoded amino acid substitutions in at least one region of the pre-S envelope protein p36 produced defects in both the production of enveloped virus and the regulation of covalently closed circular DNA (cccDNA) synthesis. Most linker substitutions, typically in the 5' two-thirds of the pre-S region of the p36 gene did not affect either cccDNA regulation or enveloped virus production but did destroy the infection competence of the enveloped particles produced. Single amino acid substitutions of residues 128 and 131 demonstrated a similar correlation between defects in the ability of p36 to support enveloped virus production and to control cccDNA levels. We concluded from these studies that virus production and cccDNA regulation probably require a common activity of p36.

Amino Acid Sequence↗
PubMed1991

Site-directed mutations in Sindbis virus E2 glycoprotein's cytoplasmic domain and the 6K protein lead to similar defects in virus assembly and budding.

Site-directed mutagenesis was used to obtain four mutants with amino acid replacements in the cytoplasmic domain of the E2 glycoprotein and three with replacements in the 6K protein of Sindbis virus. All but one of these mutants yielded progeny virus after transfection of chicken embryo fibroblasts with RNA prepared by in vitro transcription of the virus cDNA; however, even this nonproducer mutant made virus structural proteins in the transfected cells. The other six mutants divided into two groups based on growth in chicken embryo fibroblasts. One group of four mutants (two in E2 and two in 6K) was indistinguishable from wild-type in formation of infectious virus in avian cells while the other group, consisting of two mutants, grew significantly slower. All six mutants grew slower than the parental wild-type virus in mosquito cells. In avian cells, all mutants produced extracellular particles at a slower rate than the wild-type and many of the particles contained multiple nucleocapsids, based on electron microscopy and kinetics of thermal inactivation. One of the E2 mutants with a cysteine changed to alanine and the 6K mutant with four cysteines replaced were deficient in covalent-bound palmitic acid. Two mutants with changes near the signalase cleavage sites between E2 and 6K and between 6K and E1 appeared to be defective in proteolytic processing. Despite individual differences, all of these mutants and the two previously described produced similar phenotypes in which multicored infectious virus particles were released more slowly from mosquito cells than from avian cells.

Amino Acid Sequence↗