Virus degradation and nucleic acid release in single-phase phenol systems

Identification, Sequencing, and Molecular Analysis of RNA2 of Artichoke Italian Latent Virus Isolates from Known Hosts and a New Host Plant Species

Despite its first description in 1977 and numerous reports of its presence in various plant species in many countries, the molecular information available in GenBank for artichoke Italian latent virus (AILV) is still limited to a single complete genome sequence (RNA1 and 2) of a grapevine isolate (AILV-V) and a partial portion of the RNA2 sequence from an isolate of unknown origin and host. Here, we report the results of molecular analyses conducted on the RNA2 of some AILV isolates, sequenced for the first time in this study, together with the first-time identification of AILV in a new host plant species, namely chard (Beta vulgaris subsp. vulgaris), associated with vein clearing and mottling symptoms on leaves. The different AILV isolates sequenced were from artichoke (AILV-C), gladiolus (AILV-G), Sonchus (AILV-S), and chard (AILV-B). At the molecular level, the sequencing results of the RNA2 segments showed that AILV-C, AILV-G, AILV-S, and AILV-B had a length of 4629 nt (excluding the 3' terminal polyA tail), which is one nt shorter than that of the AILV-V reported in GenBank. A comparison of the RNA2 coding region sequences of all the isolates showed that AILV-V was the most divergent isolate, with the lowest sequence identities of 83.2% at the nucleotide level and 84.7% at the amino acid level. Putative intra-species sequence recombination sites were predicted among the AILV isolates, mainly involving the genomes of AILV-V, AILV-C, and AILV-B. This study adds insights into the variability of AILV and the occurrence of recombination that may condition plant infection.

Next generation sequencing and molecular analysis of artichoke Italian latent virus

Next-generation sequencing (NGS) allowed the assembly of the complete RNA-1 and RNA-2 sequences of a grapevine isolate of artichoke Italian latent virus (AILV). RNA-1 and RNA-2 are 7,338 and 4,630 nucleotides in length excluding the 3' terminal poly(A) tail, and encode two putative polyproteins of 255.8 kDa (p1) and 149.6 kDa (p2), respectively. All conserved motifs and predicted cleavage sites, typical for nepovirus polyproteins, were found in p1 and p2. AILV p1 and p2 share high amino acid identity with their homologues in beet ringspot virus (p1, 81% and p2, 71%), tomato black ring virus (p1, 79% and p2, 63%), grapevine Anatolian ringspot virus (p1, 65% and p2, 63%), and grapevine chrome mosaic virus (p1, 60% and p2, 54%), and to a lesser extent with other grapevine nepoviruses of subgroup A and C. Phylogenetic and sequence analyses, all confirmed the strict relationship of AILV with members classified in subgroup B of genus Nepovirus.

Complete sequence of RNA1 of grapevine Anatolian ringspot virus

The nucleotide sequence of RNA1 of grapevine Anatolian ringspot virus (GARSV), a nepovirus of subgroup B, was determined from cDNA clones. It is 7,288 nucleotides in length excluding the 3' terminal poly(A) tail and contains a large open reading frame (ORF), extending from nucleotides 272 to 7001, encoding a polypeptide of 2,243 amino acids with a predicted molecular mass of 250 kDa. The primary structure of the polyprotein, compared with that of other viral polyproteins, revealed the presence of all the characteristic domains of members of the order Picornavirales, i.e., the NTP-binding protein (1B(Hel)), the viral genome-linked protein (1C(VPg)), the proteinase (1D(Prot)), the RNA-dependent RNA polymerase (1E(Pol)), and of the protease cofactor (1A(Pro-cof)) shared by members of the subfamily Comovirinae within the family Secoviridae. The cleavage sites predicted within the polyprotein were found to be in agreement with those previously reported for nepoviruses of subgroup B, processing from 1A to 1E proteins of 67, 64, 3, 23 and 92 kDa, respectively. The RNA1-encoded polyprotein (p1) shared the highest amino acid sequence identity (66 %) with tomato black ring virus (TBRV) and beet ringspot virus (BRSV). The 5'- and 3'-noncoding regions (NCRs) of GARSV-RNA1 shared 89 % and 95 % nucleotide sequence identity respectively with the corresponding regions in RNA2. Phylogenetic analysis confirmed the close relationship of GARSV to members of subgroup B of the genus Nepovirus.

Grapevine deformation virus: completion of the sequence and evidence on its origin from recombination events between Grapevine fanleaf virus and Arabis mosaic virus

The complete nucleotide (nt) sequence of Grapevine deformation virus (GDefV) RNA-1 has been determined. It consists of 7386 nt, excluding the poly(A) tail, and contains a single open reading frame (ORF) encoding a polyprotein (p1) of 252 kDa. P1 comprises the 1A(Pro-cof) proteinase cofactor, the 1B(Hel) NTP-binding protein, the 1C(VPg) viral protein genome-linked, the 1D(Prot) proteinase and the 1E(Pol) RNA-dependent RNA polymerase, all of which are conserved domains in polyproteins of different members of the order Picornavirales. The amino acid (aa) sequence of GDefV RNA1 p1 has the highest identity with the homologous products of Grapevine fanleaf virus (GFLV, 86-88%) and Arabis mosaic virus (ArMV, 73-74%), two nepoviruses of subgroup A. Four cleavage sites for proteins processing were predicted (C/A, C/S, G/E and R/G) and found similar to those of GFLV RNA1. Phylogenetic trees constructed with the complete aa sequences of protein p1 and the RNA2-encoded protein p2 of GDeFV, GFLV and ArMV, showed an incongruent allocation of GDefV in these trees. Pairwise alignment and prediction of recombination sites of both RNA segments showed that GDefV RNA2 has a mosaic structure resulting from recombination events between GFLV and ArMV at the level of the 2A(HP) (homing protein), 2B(MP) (movement protein), 2C(CP) (capsid protein) and the 3'NCR (non coding region). This strongly suggests that GDefV originated from the interspecific recombination between isolates of GFLV and ArMV.

Complete nucleotide sequence and genome organisation of grapevine Bulgarian latent virus

The complete genome sequence of grapevine Bulgarian latent virus (GBLV) has been determined. RNA-1 (7,452 nt in length) contains a single ORF of 6,285 nt, encoding a polyprotein with conserved motifs characteristic of the viral protease cofactor (Prot-cofact), the NTP-binding protein (NTP), the cysteine-like protease (Cyst-Prot) and the RNA-dependent RNA polymerase (RdRp) of members of the order Picornavirales and show high aa sequence identity with blackcurrant reversion virus (BRV, 64%). RNA-2 (5,821 nt) contains a single ORF of 4,500 nt, encoding a polyprotein in which the conserved motifs of the movement protein (MP) and coat protein (CP) have been identified. The GBLV CP aa sequence shows highest homology with that of blueberry leaf mottle virus (BLMoV, 68%). Both RNAs have a poly(A) tail and a NCR at the 3' and 5' termini, respectively. The results of this study confirm the classification of GBLV as a member of a distinct species in subgroup C of the genus Nepovirus.

Molecular and Serological Characterization of Cucumber mottle virus, a New Cucurbit-Infecting Tobamo-like Virus

A new tobamo-like virus was isolated from a greenhouse-grown cucumber that showed severe mosaic distortion on leaves and fruit, in the southern part of Japan. The virus was tentatively designated Cucumber mottle virus (CuMoV) and further characterized. The size and antigenicity of the coat protein (CP) and the complete sequence of the genome were compared with those of the known cucurbit-infecting tobamoviruses: the W and SH strains of Cucumber green mottle mosaic virus (CGMMV), the C and Y strains of Kyuri green mottle mosaic virus (KGMMV), Cucumber fruit mottle mosaic virus (CFMMV), and Zucchini green mottle mosaic virus (ZGMMV). The CP of CuMoV migrated more slowly than those of CGMMV-W and -SH and KGMMV-C and -Y in sodium dodecyl sulfate polyacrylamide gel electrophoresis. In Western blot analysis, the CP of CuMoV cross-reacted weakly with antisera against CGMMV-W and did not react with antisera against KGMMV-Y. The overall nucleotide sequence of CuMoV had 62.5 to 63.5% identity with those of CGMMV-W, -SH, KGMMV-Y, CFMMV, and ZGMMV. The genome organization was characteristic of tobamoviruses, encoding a 131-kb protein, a 188-kb protein, a movement protein (MP), and CP in 5' to 3' order. In the phylogenetic analyses of the CP, CuMoV was placed in a separate lineage from CGMMV-W, -SH, KGMMV-C, -Y, CFMMV, and ZGMMV. The results indicate that CuMoV is a distinct tobamovirus species which represents a third sub-subgroup in the cucurbit-infecting tobamoviruses.

Intergeneric relationship between the Aspergillus ochraceous virus F and the Penicillium stoloniferum virus S

It was reported that the "slow" component (PsV-S) of Penicillium stoloniferum virus complex also occurred in a second genus, Aspergillus ochraceous. The responsible virus for this intergeneric occurrence was considered to be the "fast" component (AoV-F) of A. ochraceous virus complex. In this investigation, AoV dsRNA 1, that was previously shown to cross-hybridize with PsV-S dsRNA, has been cloned. It was 1754 bp in length and contained one open reading frame of 539 amino acids (p63), had the same genome organization as PsV-S dsRNA S1 and also had the conserved sequence motif of the PsV-S dsRNAs (5'-GCGCAAAA-3') at the 5' terminus. A BLAST search indicated that p63 was a putative dsRNA-dependent RNA polymerase (RdRp), had 81% of sequence homology to members of the genus Partitivirus, and grouped together with PsV-S in phylogenetic analysis. But immunoblot analysis showed that the capsid protein (P3) of AoV-F virus component did not reacted against PsV-S antiserum. These evidences suggest that the cross serological relationship between AoV-F and PsV-S previously observed may have been due to the RdRps of the respective viruses rather than between their respective capsid proteins as was assumed in 1985.

Viral properties, primary structure and phylogenetic analysis of the coat protein of an Olive latent virus 1 isolate from Olea europaea L

An Olive latent virus 1 isolate designated GM6, obtained from a Portuguese olive tree, was characterized and the coat protein gene sequenced and analysed. The purified virus particles showed to be isometric with ca. 30 nm in diameter and contained a single-stranded RNA species with ca. 3.7 kb. The dsRNA profile obtained from infected tissues showed three major species with ca. 3.7, 1.5 and 1.3 kbp. SDS-PAGE analysis revealed a major peptide with an apparent molecular mass of 32 kDa identified as the coat protein. A viral genome region containing the coat protein gene was amplified by RT-PCR and the cDNA was cloned and sequenced. The coat protein gene revealed to be 813 nucleotides long and encode a peptide with 270 amino acid residues and an estimated Mr of 29,851. Alignment of the deduced amino acid sequence with that of other necroviruses showed a higher identity with OLV-1 tulip isolate (97.7%) than with OLV-1 citrus isolate (87.7%). The consensus pattern of the coat protein 'S' domain is conserved in GM6 isolate coat protein sequence, except in amino acid 151, leucine. This is the first report on the coat protein sequence of an OLV-1 olive isolate.

Genome organization and expression of the Penicillium stoloniferum virus S

The complete sequences of two double-stranded RNAs (dsRNAs) (referred to S1 and S2) of Penicillium stoloniferum virus S (PsV-S) were established. The S1 dsRNA was 1,690 bp in length, and it contained a unique open reading frame (ORF) of 539 amino acids (molecular weight of 62 kDa, referred to P62). The S2 dsRNA was 1,523 bp in length, and also it contained one ORF of 434 amino acids (molecular weight of 47 kDa, referred to P47). Both S1 and S2 ORFs were identified only on the positive strand of each dsRNA segment. A sequence motif of (5'-CUG-3') was found at the 3'-termini of the positive strands of PsV-S1 and S2 dsRNAs. The predicted amino acid sequences of S1 dsRNA showed high sequence homology with the putative RNA-dependent RNA polymerases of RNA viruses. Near full-length and positive-sense single-stranded RNAs derived from the S1 and S2 dsRNAs were detected from the PsV-infected host cell. The expressed proteins of P62 and P47 showed a positive reaction against PsV-S antiserum in Western blot analysis. Phylogenetic analysis using the RDRP sequences and the capsid proteins of the various partitiviruses revealed that PsV-S is a definite member of the partitivirus, the family Partitiviridae, and especially clusters well along with D. destructiva virus 1 and 2.

Complete nucleotide sequence and genome organization of Grapevine fleck virus

The complete nucleotide sequence of Grapevine fleck virus (GFkV) genomic RNA was determined. The genome is 7564 nt in size, excluding the 3'-terminal poly(A) tail, is characterized by an extremely high cytosine content (ca. 50%), and contains four putative open reading frames and untranslated regions of 291 and 35 nt at the 5' and 3' ends, respectively. ORF 1 potentially encodes a 215.4 kDa polypeptide (p215), which has the conserved motifs of replication-associated proteins of positive-strand RNA viruses. ORF 2 encodes a 24.3 kDa polypeptide (p24) identified as the coat protein. ORFs 3 and 4 are located at the extreme 3' end of the viral genome and encode proline-rich proteins of 31.4 kDa (p31) and 15.9 kDa (p16), respectively, of unknown function. Phylogenetic analysis of the viral replicase and coat protein genes showed that GFkV is related to members of the Tymovirus and Marafivirus genera. Two subgenomic RNAs were present in the GFkV preparations as ascertained by molecular hybridization. The genome organization of GFkV resembles to some extent that of tymoviruses and marafiviruses. However, differences in the biological and epidemiological behaviour, cytopathology and molecular properties (i.e. size of genomic RNA and coat protein, and number of ORFs) support the notion that GFkV is a separate virus belonging in a new genus.

Nucleotide sequence of the 3' terminal region of the RNA of two filamentous grapevine viruses

The 3' terminal region of grapevine virus A (GVA) and grapevine virus B (GVB), encompassing 1883 and 2136 nucleotides, respectively, was sequenced by the deoxynucleotide chain termination method. Three putative open reading frames (ORF) were identified in both genomic viral RNAs, denoted 1 to 3 in the 5' to 3' direction. ORF 1 encoded a polypeptide with estimated M(r) of 31 kDa (GVA) and 36.5 kDa (GVB), possessing the G/D motif of the "30 K superfamily" movement proteins, and showing good alignments with putative movement proteins of trichoviruses and capilloviruses. ORF 2 was identified as the coat protein (CP) cistron, coding for polypeptides with an estimated M(r) of 21.5 kDa (GVA) and 21.6 kDa (GVB). These CPs showed substantial sequence homology with one another and with CPs of tricho- and capilloviruses, but not of closteroviruses. ORF 3 potentially coded for two small polypeptides with estimated M(r) of 10 kDa (GVA) and 14 kDa (GVB). The ORF 3 product of GVB (14 K), but not that of GVA, shared some homology with the 3' terminal polypeptides of different plant viruses that exhibit the "zinc finger domain" of proteins with nucleic acid-binding properties. GVA and GVB have many properties in common with trichoviruses but possess an extra open reading frame (ORF 3). Whether this finding may have a bearing on the classification of these viruses is unclear. However, until the taxonomic significance of this difference in genome structure is established, it seems plausible to include GVA and GVB as tentative species in the Trichovirus genus.

Messenger RNA intron in the nuclear 18s ribosomal RNA gene of deuteromycetes

Introns within messenger RNA genes have characteristic border sequences and a conserved region near the 3' end of the intron. All are involved in splicing to produce the mature mRNA. Introns in ribosomal RNA genes have less well-defined borders and contain no internal conservation. We report here mRNA-type introns located near the 3' end of the 18s rRNA genes of the deuteromycetes Phialophora americana and Cenococcum geophilum. Inserted sequences of various sizes have also been located at the same point in several other deuteromycete species.

Properties of a filamentous virus isolated from grapevines affected by corky bark

A virus with highly flexuous filamentous particles c. 800 nm long, showing distinct transverse striations was isolated with high frequency (60%) by inoculation of Nicotiana occidentalis with sap from grapevine accessions indexing positive for corky bark. The virus, for which the name grapevine virus B (GVB) is proposed, has an ssRNA genome with mol. wt. of c. 2.5 x 10(6) Da (c. 7600 nt) and coat protein subunits with mol. wt. of c 23,000 Da. GVB has a very restricted herbaceous host range and was experimentally transmitted by the mealybug Pseudococcus ficus. The physicochemical and ultrastructural properties of GVB resemble those of closteroviruses. However, it is serologically unrelated to other grapevine closteroviruses including grapevine virus A, with which it shares some biological and physicochemical properties.

Properties of a previously undescribed grapevine nepovirus from Tunisia

A virus with isometric particles c. 30 nm in diameter and angular contour was isolated by inoculation of sap from a Tunisian grapevine with mild mottling and leaf deformation. The virus sedimented in sucrose density gradients as three components: T (empty shells), M (particles containing a molecule of ssRNA with an apparent size of 5,800 nucleotides, constituting 35% of the particle weight) and B (particles containing a molecule of ssRNA with apparent size of 6,800 nucleotides, constituting 41% of the particle weight). Virus particles had buoyant densities of 1.31 (T), 1.45 (M), and 1.49 g/cm3 (B) in cesium chloride equilibrium gradients. The coat protein subunits consisted of a single polypeptide with mol. wt. of c. 59,000 daltons. An antiserum was produced with a titer of 1:256, which did not react with healthy plant antigens. Cells of artificially infected herbaceous hosts showed cytoplasmic vesiculate-vacuolate inclusion bodies, virus-containing tubules, mostly associated with plasmodesmata and/or cell wall protrusions, and crystalline aggregates of virus particles and empty capsids. The physicochemical and ultrastructural properties of this virus resemble very much those of nepoviruses. However, it was serologically unrelated to 19 different members of the group, including all those reported to infect grapevines. Therefore, the virus is possibly a hitherto unreported nepovirus for which the name of grapevine Tunisian ringspot virus (GTRV) is proposed.

Murine immunosuppression with mycoviral dsRNA

The effect of three different size molecular weight species of mycoviral dsRNA on the immune response to sRBC was tested in C57Bl/6 mice. The various dsRNA species were extracted from electrophoresis polyacrylamide-agarose slab gels. Their molecular weights ranged from 1.0 x 10(6) daltons to 3.5 x 10(6) daltons. All three sizes of mycoviral dsRNA significantly (p less than 0.0001) suppressed the hemolytic antibody titer of mice 8 days after immunizations with 15 micrograms dsRNA/mouse and 10(8) sRBC when compared to control mice which received only sRBC. No immune suppression was observed in any of the mice challenged with a second sRBC immunization 60 days after the first inoculations. Hemagglutination titers at this time were typical of a secondary antibody response to sRBC. In conclusion these three molecular weight mycoviral dsRNA species appeared to be potent immunosuppressors when approximately 15 micrograms/mouse were used.

Rapid, simple method of preparing rotaviral double-stranded ribonucleic acid for analysis by polyacrylamide gel electrophoresis

A procedure for extracting rotaviral double-stranded ribonucleic acid (RNA) directly from fecal and intestinal specimens collected from calves and pigs is described. This procedure provides a rapid, simple, reproducible method of obtaining rotaviral double-stranded RNA preparations suitable for electrophoretic analysis in polyacrylamide-agarose composite gels. The rotaviral genome electrophoretic migration pattern produced by double-stranded RNA extracted directly from a specimen by this procedure was qualitatively identical to the electrophoretic migration pattern obtained with double-stranded RNA extracted from purified rotavirus derived from the same specimen. Direct extraction of specimens containing porcine rotavirus-like virus by this procedure gave preparations that had electrophoretic migration patterns similar, but not identical, to the characteristic electrophoretic migration pattern of the rotaviral genome. Sufficient rotaviral double-stranded RNA could be extracted from 6 ml of fecal or intestinal specimen by this procedure to permit 15 or more electrophoretic assays.

Complex of Virus-Like Particles Containing Double-Stranded RNA from Thielaviopsis basicola

Six randomly selected isolates of Thielaviopsis basicola were found to contain spherical virus-like particles (VLPs) approximately 40 nm in diameter. One isolate, ATCC 34114, selected for further analysis contained a complex of VLPs that sedimented as eight or more bands in sucrose density gradients and contained five size classes of double-stranded RNA. Five discrete precipitation lines were obtained in immunoelectrophoresis, which indicated that this isolate of T. basicola contains five distinct species of VLPs.

The buoyant density of three double-stranded RNAs in cesium sulfate

The buoyant densities in Cs2SO4 of the double-stranded RNA from the bacteriophage phi 6 and the virus-like particles of Helminthosporium maydis and Penicillium chrysogenum were determined by a Taylor series expansion and by the position and slope of the gradient relative to the isopycnic position (hinge point method). Buoyant densities for the three types of double-stranded RNA calculated by the two methods were, respectively, 1.6089 and 1.6083, 1.6065 and 1.6059 and 1.6057 and 1.6050.

The electrophoretic mobility of double-stranded RNA in polyacrylamide gels as a function of molecular weight

A re-evaluation of the mobility of double-stranded RNA on polyacrylamide gels over a molecular weight range of 0.46-6.3 . 10(6) was carried out using double-stranded RNAs of: bacteriophage ø6; virus like particles or mycoviruses of Penicillium chyrsogenum, Penicillium stoloniferum and Helminthosporium maydis, and reovirus type III. When the relative mobility on polyacrylamide gels was plotted as a function of log molecular weight, a smooth curve could be drawn which passed through all points. The implications of these findings to the determination of molecular weight of double-stranded RNA by polyacrylamide gel electrophoresis are discussed.

Action of nucleases on double-stranded RNA

Double-stranded RNAs from Penicillium chrysogenum virus have been treated with RNAse III, pancreatic RNAse A and RNAse T1 and the degradation of the RNAs has been studied under different conditions. It was found that only the two former enzymes cut across both strands, RNase T1 cannot cleave double strands. RNase III was shown to digest double-stranded RNA by a two step process: an initial phase of specific cleavage is followed by random degradation. In the first phase the enzyme exhibited a definite preference for some specific base pattern. Partial or complete degradation with pancreatic RNase A could also be achieved in media with high salt concentration provided that the enzyme: substrate ratio was increased together with the salt concentration. By combining different assay techniques, the process of degradation was followed from the early stages to complete digestion and the breakdown products were characterised. It is suggested that a structural change in the enzyme molecules enables them to act on double-stranded RNA. RNAse T1, being unable to cleave double strands, provides a useful tool for studying the secondary structure of RNA molecules. Treatment with different nucleases yielded some new information on the structure of different RNA species in Penicillium stoloniferum virus.

Base composition and hybridization studies of the three double-stranded RNA segments of bacteriophage phi 6

The three double-stranded ribonucleic acid (dsRNA) segments of the bacteriophage phi6 were isolated and shown to have similar melting temperatures and base compositions. RNA:RNA hybridization experiments with the isolated segments eliminate the possibility that the two smaller dsRNA segments arise from a cleavage of the large dsRNA segment. The two smaller RNA segments reanneal rapidly even at low temperatures; in contrast, the large dsRNA reannealed only at higher temperatures. Evidence is also presented which suggests that the dsRNAs may contain a short single-stranded RNA tail.

In vitro photoreactivation of ultraviolet-inactivated ribonucleic acid from tobacco mosaic virus

Abstract— Treatment of ultraviolet‐inactivated tobacco mosaic virus ribonucleic acid (TMV–RNA) with extracts obtained from the local lesion host, Nicotiana tabacum var. Xanthi, n.c., and simultaneous illumination at 365 nm results in up to a four‐fold increase in infectivity over non‐illuminated controls. The active material in the extract appears to be associated with protein, based on its inactivation by boiling, precipitation with ammonium sulfate, and exclusion from Bio‐Rad P100 polyacrylamide. Partially purified DNA photoreactivating enzyme from yeast or pinto bean has no activity on ultraviolet‐irradiated TMV–RNA.

Proteinaceous virus-like particles from an isolate of Aspergillus flavus

Virus-like particles were purified from a single nonaflatoxin-producing isolate of Aspergillus flavus. The virus-like particles were spherical, measuring 27 to 30 nm in diameter, were electrophoretically homogeneous, and sedimented at approximately 49S. The particles had a buoyant density of 1.28 g/cm(3) in CsCl and contained no detectable nucleic acid.

RNA polymerase activity associated with bacteriophage phi 6

The Pseudomonas phaseolicola bacteriophage phi6 incorporated labeled UTP into an acid-insoluble precipitate. Incorporation was dependent on the presence of manganese acetate, ATP, GTP, CTP, and a short heat treatment of the phage; the reaction was stimulated by NH(4)Cl. The substitution of (14)C-ATP, -CTP or -GTP for UTP, together with the appropriate unlabeled ribonucleoside triphosphates, disclosed that CMP was incorporated to the greatest extent followed by GMP, UMP, and AMP. Radioactive RNAs formed by the reaction were resistant to RNases A and T(1) in high salt but susceptible to these nucleases in low salt. The labeled RNA co-sedimented and co-electrophoresed with phi6 double-stranded (ds) RNA. However, the distribution of the radioactivity into the three ds-RNA components varied depending on the (14)C-ribonucleoside triphosphate used in the reaction. The incorporation of UMP was primarily into the two smaller ds-RNA segments, GMP primarily into the large ds-RNA segment, and CMP and AMP were about equally distributed into all three ds-RNA segments.