The results of the meetings of the International Committee on Taxonomy of Viruses, held in Madrid, September 1975, are briefly reported: rules of viral nomenclature, composition of the new Executive Committee, and a list of the names so far officially agreed. Introduction The International Committee on the Taxonomy of Viruses (ICTV), which is a committee of the Section on Virology of the International Association of Microbiological Societies (IAMS), completed a round of meetings during the Third International Congress for Virology that was held in Madrid from September 10--17, 1975. Since ICTV only meets during these conferences, which are held every four years, the meetings are important occasions for reviewing the classification and nomenclature of viruses. Decisions on new names, which encapsulate the recognition of natural "groups" of viruses, evolve slowly. Official approval for new names depends upon a series of sequential steps ; recommendations by one or more of the subcommittees of the Executive Committee of ICTV (subcommittees on Bacterial, Invertebrate, Plant and Vertebrate Viruses respectively, and for some of the larger viral groups which span several kinds of hos t s the Coordination Subcommittee), which are considered by the Executive Committee of ICTV and may finally be submitted for approval by ICTV itself. Only after this final approval does a name become "official". The results of the last five years of work by ICTV and its committees will be published early this year as a separate volume of "Intervirology", the official journal of the Section on Virology of IAMS, and additional copies will be produced for sale as separates. This "Second P~eport" will include, besides "approved" and common names of virus groups, a brief description of the properties of each

Classification and Nomenclature of Viruses

Using freshly isolated maize mesophyll protoplasts and a transient expression method, I showed that the transcriptional activity of seven maize photosynthetic gene promoters is specifically and coordinately repressed by the photosynthetic end products sucrose and glucose and by the exogenous carbon source acetate. Analysis of deleted, mutated, and hybrid promoters showed that sugars and acetate inhibit the activity of distinct positive upstream regulatory elements without a common consensus. The metabolic repression of photosynthetic genes overrides other forms of regulation, e.g., light, tissue type, and developmental stage. Repression by sugars and repression by acetate are mediated by different mechanisms. The identification of conditions that avoid sugar repression overcomes a major obstacle to the study of photosynthetic gene regulation in higher plants.

Metabolic repression of transcription in higher plants.

Mechanism of capsid assembly for an icosahedral plant virus.

The coat protein (CP) of alfalfa mosaic virus was used as a carrier molecule to express antigenic peptides from rabies virus and HIV. The antigens were separately cloned into the reading frame of alfalfa mosaic virus CP and placed under the control of the subgenomic promoter of tobacco mosaic virus CP in the 30BRz vector. The in vitro transcripts of recombinant virus with sequences encoding the antigenic peptides were synthesized from DNA constructs and used to inoculate tobacco plants. The plant-produced protein (virus particles) was purified and used for immunization of mice. Both antigens elicited specific virus-neutralizing antibodies in immunized mice.

https://www.pnas.org/content/pnas/94/11/5784.full.pdf

Antigens produced in plants by infection with chimeric plant viruses immunize against rabies virus and HIV-1

The helicase-like 1a and polymerase-like 2a proteins of brome mosaic virus (BMV) are required for viral RNA replication in vivo, are present in membrane-bound viral RNA polymerase extracts, and share conservation with the many other members of the alphavirus-like superfamily. To better understand BMV RNA replication and BMV-host interactions, we used confocal microscopy and double-label immunofluorescence to determine and compare the sites of 1a, 2a, and nascent viral RNA accumulation in BMV-infected barley protoplasts. 1a and 2a showed nearly complete colocalization throughout infection, accumulating in defined cytoplasmic spots usually adjacent to or surrounding the nucleus. These spots grew throughout infection and by 16 h postinoculation often assumed a vesicle-like appearance. The BMV RNA replication complex incorporated 5-bromouridine 5'-triphosphate into RNA in vitro and in vivo, allowing immunofluorescent detection of nascent RNA. The cytoplasmic sites of BMV-specific RNA synthesis coincided with the sites of 1a and 2a accumulation, and at the resolution of confocal microscopy, all sites of 1a and 2a accumulation were sites of BMV RNA synthesis. Double-label immunofluorescence detection of selected subcellular markers and 1a or 2a showed that BMV replication complexes were tightly associated with markers for the endoplasmic reticulum but not the medial Golgi or later compartments of the cellular secretory pathway. Defining this association of BMV RNA replication complexes with endoplasmic reticulum markers should assist in identifying and characterizing host factors involved in BMV RNA replication.

/pdf/brome-mosaic-virus-helicase-and-polymerase-like-proteins-1t85po194g.pdf

Brome mosaic virus helicase- and polymerase-like proteins colocalize on the endoplasmic reticulum at sites of viral RNA synthesis.

Summary
The rates of virus RNA synthesis and virion accumulation were investigated in brome mosaic virus-infected barley protoplasts. Single-stranded virus RNAs could be detected as early as 6 h after inoculation. Only RNA components 1 and 2 were detected at this time, suggesting that their synthesis is initiated relatively early in infection. The RNAs were synthesized at similar rates from 16 to 35 h post inoculation with maximal synthesis until approx. 25 h after inoculation. Double-stranded replicative forms of the four virus RNAs were observed. Their synthesis was first detectable at 6 h post inoculation and followed a time course similar to that of the single-stranded RNA species. Analysis of RNA encapsidation and infectivity assays of protoplast homogenates revealed that virion formation was greatest between 10 and 25 h after inoculation. All four RNAs were present in virions at 10 h post inoculation. Particles containing RNA 3 and RNA 4 accumulated at a faster rate than particles containing RNA 1 or RNA 2.

T. C. Hall

Papers

Synthesis, accumulation and encapsidation of individual brome mosaic virus RNA components in barley protoplasts.