Viruslike particles containing knob-associated histidine-rich protein are secreted into the culture medium of Plasmodium falciparum in vitro cultures.

This report describes the isolation of a viruslike particle from in vitro cultures of the human malaria parasite P. falciparum. Electronmicroscopic observations suggest that the particles are liberated into the culture medium by budding from the erythrocyte membrane. The density of the free particles is 1.16, they contain nucleic acid and two distinct molecular species of the knob-associated Histidine-rich protein. Proteins of the particles are recognized by sera from malaria patients. The previously described knobs may correspond to viral coats inserted in the membrane.

[Isolation of virus-like particles of in vitro cultures of Plasmodium falciparum]. / Isolement de particules de type viral dans les cultures in vitro de Plasmodium falciparum.

We have isolated virus-like particles from in vitro cultures of the malarial agent Plasmodium falciparum. These particles have a buoyant density of 1.16 g/cm3, contain DNA, and appear to arise from budding structures on the surface of parasitized erythrocytes.

[Change in the envelope of a murine retrovirus produced in the presence of toyocamycin]. / Modification de l'enveloppe d'un retrovirus murin synthétisé en présence de toyocamycine.

Toyocamycin (TMC), an adenosine analog, impairs qualitatively and quantitatively virus production in a cellular system chronically infected by Friend Virus. Viral particles released by cell cultures treated with 0.2 microgram/ml of the drug have lost most of their glycoprotein (gp 70) content. This phenomenon is likely to modify the viral envelope and could explain the loss of infectivity of the virus.

[Production of Friend virus particles at the surface of cells synchronized by Ficoll gradient centrifugation]. / Production de particules du virus de Friend à la surface de cellules synchronisées par centrifugation en gradient de Ficoll.

Murine cells continuously producing Friend viral complex were synchronized by Ficoll gradient centrifugation. Cells were isolated from different parts of the gradient and counts of budding particles were performed on ultra-thin sections. No significant differences were noticed, suggesting that viral release is not related to cell cycle.

Replication of Mouse Sarcoma Virus (Moloney) and its helper in a human heteroploid cell line of malignant origin.

A human heteroploid cell line of malignant origin (J111) was infected with Mouse Moloney Sarcoma Virus. [MSV-M(MLV)]. The replication of the virus was demonstrated by different methods. After a few passages of infected cultures, the transforming component of MSV-M(MLV) disappeared from the supernatant fluids and cells. The non transforming helper component continued to be produced. The relatively low amount of helper virus released by the cells suggests a control of its replication in the J111 cellular system.

[Viral RNAs from cells infected by an oncornavirus. I. Characterization of viral RNAs associated with cytoplasmic particles]. / RNAs viraux des cellules infectées par un oncornavirus: I. - Caractérisation des RNAs viraux associés à des particules cytoplasmiques.

Oncornaviral particles on the way of their synthesis have been isolated from cytoplasm of a Friend virus-producing murine cell line. By use of electron microscopy and retrotranscriptase assay, it was found that the majority of the viral structures is pelleted by sedimentation at 90.000 g. The Poly (A) RNA of this pellet contains principally 70S and 35S RNA species which, as judged by size determination and hybridization with Friend-virus c-DNA are the species embedded into the virions. We verified that conditions which were used in the course of isolation, effectively dissociate polysomes and prevent them from co-sedimenting with viruses.

[Demonstration of circular ribonucleic acid in the Lumbo virus (Bunyavirus)]. / Mise en évidence de molécules d'acide ribonucléique circulaire dans le virus Lumbo (Bunyavirus)

Electron microscopy study of RNA extracted from Lumbovirus shows the existence of circular molecules, which are not susceptible to thermal or chemical denaturation. These facts suggest that the RNA is present inside the virion in a covalently closed circular form.