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SUMMARYA sequence of 5987 nucleotides is reported for the RNA of potato leafroll luteovirus (PLRV). The sequence contains six large open reading flames, and non-coding regions of 174 nucleotides at the 5' end, 141 nucleotides at the 3' end and 197 nucleotides between two large blocks of coding sequences. The 5' coding region encodes two polypeptides of 28 000 (28K) and 70K which overlap in different reading frames and circumstantial evidence suggests that the third open reading frame in the 5' block is translated by frameshift readthrough near the end of the 70K polypeptide to give a l18K polypeptide. The C-terminal part of the l18K protein contains the consensus sequence for RNA-dependent RNA polymerases. In vitro translation of PLRV RNA resulted in the synthesis mainly of 28K and 70K polypeptides and the largest product made was about 125K; these sizes are similar to those predicted for the translation products of the 5' block of coding sequence. The 3' block of coding sequence codes for three polypeptides: a 23K coat protein, a 17K polypeptide which is encoded in a different frame, and a 53K polypeptide which immediately follows the coat protein coding sequence, and is in the same reading frame. Circumstantial evidence suggests that the 53K polypeptide is translated by readthrough of the amber termination codon of the coat protein gene. The amino acid sequences encoded by the 3' block of coding sequence show many similarities with analogous polypeptides translated from the nucleotide sequences of RNA of barley yellow dwarf virus, PAV strain (BYDV) and,

This report describes the taxa and member viruses approved by the ICTV between 1970 and 1993. Descriptions of the most important characteristics of these taxa are provided, together with a list of members and selected references. These descriptions represent the work of the chairpersons and members of the Subcommittees and Study Groups of the ICTV. A glossary of abbreviations and terms is provided first; followed by a set of virus diagrams and listings of the taxa, alphabetically, then by host, and then by nucleic acid and genome characteristics. A key to the placement of the viruses in the taxa is provided. Descriptions of the taxa and a listing of unassigned viruses follow.The names of orders, families and genera approved by ICTV are printed in italics. Names that have not yet been approved are printed in quotation marks in standard type. Vernacular species names, whether approved or not, are printed in standard type.Throughout the Report, three categories of member viruses of the various taxa have been defined: (1) Type species: pertains to the type species used in defining the taxon. As noted above, the choice of the type species by ICTV is not made with the kind of precision that must be used by international specialty groups and culture collections or when choosing substrates for vaccines, diagnostic reagents, etc. In this regard, the designation of prototype viruses and strains must be seen as a primary responsibility of international specialty groups. (2) Other species: pertains to those viruses which on the basis of all present evidence definitely belong to the taxon. (3) Tentative species: pertains to those viruses for which there is presumptive but not conclusive evidence favoring membership of the taxon.The ICTV has approved one order, 50 families, 9 subfamilies and 164 genera. Descriptions of virus satellites, viroids and the agents of spongiform encephalopathies (prions) of humans and several animal species are included. Finally a list of unassigned viruses is provided with a pertinent reference for each. In the synthesis of viral RNA, the term polymerase has been replaced in general by two somewhat more specific terms: RNA replicase and RNA transcriptase. The term transcriptase has become associated with the enzyme involved in messenger RNA synthesis, most recently with those polymerases which are virion-associated. However, it should be borne in mind that for some viruses it has yet to be established whether or not the replicase and transcriptase activities reflect distinct enzymes rather than alternative activities of a single enzyme. Confusion also arises in the case of the small positive-sense RNA viruses where the term replicase (e.g., Q~ replicase) has been used for the enzyme capable both of transcribing the genome into messenger RNA via an intermediate negative-sense strand and of synthesizing the genome strand from the same template. In the text, the term replicase will be restricted as far as possible to the enzyme synthesizing progeny viral strands of either polarity. The term transcri...

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