- Volume 10, Issue 1, 1971

Influenza virus plus and minus strand RNA complexed with RNP-antigen protein quite efficiently, while double-stranded virus RNA was not significantly bound. Sindbis and Newcastle disease virus RNA attached to a much lower degree. A small AMP-rich RNA fraction of uninfected cells also formed a complex with the virus RNP-antigen protein.

Injection of mice with mouse brain suspensions of lymphocytic choriomeningitis virus produced a non-specific virus inhibitor which required 48 to 72 hr to act in monkey kidney and HeLa cell cultures. Like interferon it was active against numerous RNA viruses, was non-sedimentable, was unaffected by antiserum to lymphocytic choriomeningitis virus, and showed a dose—response effect. However, unlike interferon it was acid-labile, crossed species barriers, and was eliminated by changing the medium at the time of virus challenge. Mouse brain preparations freed of detectable virus by ultracentrifugation had properties similar to preparations containing lymphocytic choriomeningitis virus. Furthermore, tissue culture fluids containing lymphocytic choriomeningitis virus contained no inhibitor. Tissues of mice infected with the we strain of lymphocytic choriomeningitis virus also contained no inhibitor. Hence, this inhibitor appears to represent a new class of broad spectrum virus inhibitor that may be useful for the characterization of lymphocytic choriomeningitis virus strains.

The defective adenovirus-associated viruses produce infectious progeny only in cells co-infected with an unrelated helper adenovirus. However, the adenovirus-associated viruses produce antigen detectable by immunofluorescence but not infectious virus in cells co-infected with herpes simplex virus. This incomplete helper effect provided by herpes simplex virus was studied in Hep-2 cells by quantitative kinetic procedures. Dose response studies showed that a single infectious adenovirus associated virus-1 particle and a single infectious herpes simplex virus particle were sufficient to initiate adenovirus-associated virus antigen synthesis. Adenovirus-associated virus-1 antigen was formed 6 hr after infection with both viruses, and at a time before the production of infectious herpes simplex virus. Co-infected cells, deprived of arginine, formed adenovirus-associated virus-1 antigen while undergoing an abortive herpes simplex virus infection in which infectious herpes simplex virus was not produced.

Sequential inoculation studies showed that the 6 hr latent period for adenovirus-associated virus antigen formation was lengthened, rather than shortened, by pre-infection with herpes simplex virus. Cytosine arabinoside treatment of co-infected cells within 4 to 6 hr after infection prevented adenovirus-associated virus antigen formation.

The use of less conventional methods of virus preparation for electron microscopy (i.e. freeze-drying and freeze-etching) showed that the influenza virus particles are more uniform than has generally been assumed. Their shape resembles an icosahedron with an average ‘diameter’ of 1080 Å. The surface projections (spikes) are arranged mostly in equilateral triangles, often building hexons and, in a few cases, pentons as well. Freeze-etching revealed the inside of some particles, particularly in the case of long filaments. We arrived at the following general concept of virus structure: the nucleoprotein coil, either cylindrical or spherical, is enveloped by a membrane bearing spiky macromolecules, probably of different structure and function. The membrane with spikes is called the envelope. The centre-to-centre distance of the spikes ranges from 70 to 90 Å, depending on the mode of preparation for electron microscopy. The innermost space of the virus particle is probably filled with a liquid, as is apparent from the change in form after normal drying and also from freeze-etching.

The nucleoprotein helix consists of threads about 70 Å thick having an internal channel of about 10 Å. The number of threads is usually a multiple of 3, such as 6, 9, 12 or 30 etc.

Polyoma virus demonstrated a requirement for all of the individual amino acids of Eagle’s minimal essential medium; however, arginine deprivation inhibited virus synthesis to the greatest extent. Early recovery of virus synthesis upon addition of arginine to an arginine-deprived infection indicated that arginine deprivation possibly inhibited a late step of virus synthesis. Arginine deprivation inhibited polyoma virus DNA synthesis by 60%, whereas plaque-forming activity was inhibited approximately 90% during the same period. Arginine deprivation did not affect the number of cells synthesizing structural antigens; however, the encapsidation of virus DNA, dependent upon the synthesis of all structural proteins necessary for virus maturation, was inhibited approximately 90%. A portion of the particles synthesized in arginine-deprived cultures was susceptible to nuclease digestion suggesting incomplete assembly.

Cytoplasmic inclusions (X-bodies) in coriander leaf cells infected with parsnip mosaic virus contained much endoplasmic reticulum and many Golgi bodies, together with cylindrical inclusions which, depending on the plane of sectioning appeared as bundles or pinwheels with attached laminated aggregates. The pinwheels differed from those associated with several other filamentous viruses because the radiating plates forming their arms were exceptionally long and flexuous. These plates were frequently attached to the plasmalemma or to elements of the endoplasmic reticulum. In its effects on cells, parsnip mosaic virus thus resembles other members of the potato virus Y group.

Atropa mild mosaic virus is transmissible from tobacco to tobacco, both by green peach aphids and by inoculation of sap. It causes mosaic symptoms and has elongated slightly flexuous particles with a modal length of about 925 nm. It induces the formation of pinwheels resembling those elicited by viruses of the potato Y group (potyviruses), and infected cells also contain crystalline structures resembling hexagonal arrays of tubules.

A particulate cell-free fraction of barley leaves infected with brome mosaic virus had RNA polymerase activity in the presence of actinomycin D and EDTA. The RNA produced during a short pulse (3½ min.) of 3H-labelled UTP was mostly resistant to RNase in high salt concentration, whereas longer labelling periods gave an increasingly RNase-sensitive product. ‘Pulse-chase’ experiments showed that the first product labelled sedimented at about 14 s, was presumably a double-stranded RNA and was the precursor of single-stranded RNA, most of which sedimented more slowly. Production of the single-stranded RNA depended upon the presence of all four ribonucleotides. Little complete radioactive brome mosaic virus RNA could be found, possibly because of the effect of nucleases in the reaction mixture. When heated, the 14 s RNase-resistant RNA gave polydisperse single-stranded RNA, some of which sedimented at a similar rate to the large component of brome mosaic virus RNA. Most of the RNase-resistant RNA did not behave like replicative intermediates that have been described.