In vitro transcription of wound tumor virus RNA by virion-associated RNA transcriptase

Expression of wound tumor virus gene products in vivo and in vitro

Infection of Agallia constricta vector cell monolayers with wound tumor virus results in the synthesis of 12 virus-specific polypeptides. Confirmation that these polypeptides are virus encoded rather than virus induced was obtained by cell-free translation of in vitro synthesized viral mRNA. In addition, transcription by purified wound tumor virus particles was coupled with translation of the resulting transcripts in a wheat embryo cell-free extract. Six previously described structural polypeptides, one presumptive structural polypeptide, and five previously unidentified nonstructural polypeptides were synthesized in infected vector cell monolayers, in cell-free extracts directed by in vitro synthesized viral mRNA, and in the homologous plant cell-free system, in which viral transcription was coupled with translation. Pulse-chase experiments revealed no evidence of precursor-product relationships for the wound tumor virus-specific polypeptides.

Molecular cloning and characterization of the genome of wound tumor virus: a tumor-inducing plant reovirus

The double-stranded RNA genome of the tumor-inducing plant pathogen, wound tumor virus, was converted to double-stranded DNA and cloned into plasmid pBR322. Multiple apparent full-length copies of 9 of the 12 wound tumor virus genome segments were identified. The entire sequence of cloned genome segment S12, the smallest of the genome segments, was determined. This genome segment was found to be 851 nucleotides in length and to possess a single long open reading frame that extends 178 codons from the first AUG triplet (residues 35-37): information sufficient to encode a protein of the size estimated for the smallest of the previously identified wound tumor virus primary gene products, Pns 12. Sequence data obtained from analysis of cloned cDNA copies of several genome segments and from direct analysis of the 3' termini of the double-stranded genome RNAs revealed that each wound tumor virus genome segment possesses the common terminal sequences: (+) 5'GGUAUU ... UGAU 3' (-) 3'CCAUAA ... ACUA 5'.

Variant dsRNAs associated with transmission-defective isolates of wound tumor virus represent terminally conserved remnants of genome segments

Variant double-stranded RNAs are often associated with the genome of transmission-defective isolates of wound tumor virus. These RNAs are replicated and packaged into virus particles in systemically infected plants and are transcribed in vitro by the virion-associated transcriptase. Direct physical evidence that the variant RNAs are remnants of particular WTV genome segments was provided by molecular hybridization studies. Subsequently, ribonuclease T1 digestion products of 3'-end-labeled genome and remnant RNAs were analyzed by one- and two-dimensional electrophoretic techniques. One-dimensional partial and complete digestion patterns were indistinguishable, indicating that the guanosine positions relative to the 3' terminus of the corresponding strands of a particular genome segment and its remnant RNA are the same for at least 40 nucleotides from each end. Fingerprints of the 3' terminal ribonuclease T1-resistant fragments were identical, showing that the nucleotide composition of the 3' terminal ends of the corresponding strands of a particular genome segment and its remnant RNA are also identical. These results indicate that variant RNAs associated with transmission-defective WTV isolates are formed by deletion of an internal portion (as much as 85%) of genomic RNA segments yielding terminally conserved genomic remnants that are functional with respect to transcription, replication, and packaging.

In Vitro Synthesis and Modification of mRNA by Exvectorial Isolates of Wound Tumor Virus

Nontransmissible (exvectorial) isolates of wound tumor virus retain the ability to catalyze in vitro synthesis of RNA. Furthermore, exvectorial virus particles exhibit mRNA-2′- O -methyltransferase activity even after long-term (30-year) passage in a host that lacks this enzyme activity.