Messenger activity of RNA transcribed in vitro by DNA-RNA polymerase associated to vaccinia virus cores

Dinucleotide Sequences at the 5' Ends of Vaccinia Virus mRNA's Synthesized In Vitro

The diversity of dinucleotide sequences at the 5' ends of vaccinia virus mRNA's was determined by a two-dimensional electrophoresis procedure. RNA labeled with S-adenosyl[methyl-(3)H]methionine was synthesized in vitro by enzymes present in vaccinia virus cores. The RNA, ending in m(7)G(5')pppN(m)pN-, was beta-eliminated and treated with alkaline phosphatase. After digestion with RNases T(2), T(1), and A, all eight possible dinucleotides containing G(m) and A(m) were identified. They are, in decreasing order of abundance: G(m)pUp (22%), A(m)pCp (18%), G(m)pAp (16%), G(m)pCp (15%), A(m)pAp (11%), A(m)pUp (10%), A(m)pGp (7%), and G(m)pGp (2%).

Polyamines stimulate DNA-dependent RNA synthesis catalyzed by vaccinia virus

The RNA synthesis in purified vaccinia virus can occur in the presence of either Mg2+ or Mn2+ if polyamine (spermidine or spermine) is present in the assay system. Under our assay conditions transcription was linear up to 30 min and the RNAs synthesized had a sedimentation coefficient of about 8 to 12 S. We also prepared a virus extract from purified vaccinia virus and tested for in vitro transcription. The soluble transcription system was dependent on the addition of exogenous DNA and single-stranded DNA was a more effective template than double-stranded. In the presence of polyamine and Mg2+ or Mn2+ the viral RNA polymerase was active in the transcription of total native vaccinia DNA and a small fragment cloned in pBR322.

Translation of vaccinia virus and cellular mRNA in cell-free systems prepared from uninfected and vaccinia virus infected L929 cells

Cell-free translation systems were prepared from uninfected and vaccinia infected (3 and 5 hours post-infection) L929 cells. The systems were made mRNA dependent in order to translate exogenous mRNA mixtures. The overall rate of protein synthesis was similar in the three translation systems. However, one-dimensional electrophoresis showed that the systems differed in terms of the translation efficiency for individual mRNAs. This could be demonstrated with each of the following mRNA mixtures: early vaccinia mRNA synthesized by vaccinia cores in vitro, mRNA isolated from polysomes of vaccinia infected HeLa cells ("late" vaccinia mRNA) and cytoplasmic ascites mRNA. When the above mentioned groups of mRNAs were allowed to compete for translation in the cell-free systems and their products were analyzed on one-dimensional gels, the following order of translational efficiency was observed: the most prominent species of vaccinia early mRNA (other species could not be judged) were translated better than some late vaccinia mRNA species which in turn were slightly more efficiently translated than cellular mRNAs.

Structural proteins and cell-free translation products of total RNA and hybrid-selected RNA from two DNA variants of vaccinia virus

Two major variants of vaccinia virus, large (L) and small (S), differ by a deletion of 9.7 kilobase pairs. The structural proteins and the translation products of RNA transcribed in vitro from each of these variants were analyzed by gel electrophoresis. Recombinant plasmids were used to select RNA transcribed from the L variant sequences corresponding to the deletion. This RNA yielded translation products indicating that a minimum of 11 polypeptides, including two structural proteins, map within the deletion.

Expression of vaccinia virus early mRNA in Ehrlich ascites tumor cells. 1. Translation of cellular and viral early mRNA in cell-free systems from uninfected and virus-infected cells at the early stage

Translation of cellular and early vaccinia RNA in nuclease-treated lysates, derived from uninfected and vaccinia-virus-infected cells at the early stage, has been investigated. When using limiting amounts of RNA no discrimination of translation was observed in the infected cells lysates; this conclusion was confirmed by sensitive RNA competition experiments for translation in vitro and also when using two different fractionated systems for protein synthesis in vitro. This absence of detectable discrimination in vitro was established both by comparing incorporation of [35S]methionine into proteins and by analysis of the products thus synthesized by sodium dodecylsulfate gel electrophoresis. However, a modification of the translational machinery from vaccinia-virus-infected cells did occur since the only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis l machinery from vaccinia-virus-infected cells did occur since the only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis l machinery from vaccinia-virus-infected cells did occur since the only the ribosomal salt wash derived from infected cells was able to reverse the inhibition of protein synthesis in vitro resulting from excess RNA (control or early). This property of vaccinia-virus-infected cell lysates may result from the synthesis of an early protein involved in translation or from a better recovery of translational factors from the infected cells, as suggested in the accompanying paper.

Organization and expression of the poxvirus genome

Poxviruses comprise a large group of very complex animal DNA viruses which replicate in the cytoplasm of infected cells. Vaccinia virus, the most studied poxvirus, has a linear, double stranded DNA genome with an approximate molecular weight of 120 x 10(6) (180 kilobase pairs). The two strands of the DNA molecule are naturally cross-linked at both termini. In addition, the vaccinia virus genome contains very long inverted terminal repetitions of approximately 10 kilobase pairs which are further characterized by the presence of direct tandem repeats of a 70-base-pair sequence arranged in two blocks of 13 and 17 copies, respectively. A central region of the genome is highly conserved between different orthopoxviruses. In contrast, the ends are hypervariable and may contain extensive deletions and complex, symmetrical sequences rearrangements. Vaccinia virus gene expression is divided into two stages. Early in infection, RNA complementary to one half of one strand-equivalent of the genome is transcribed within subviral particles by the virion-associated RNA polymerase. Later in infection, after DNA replication, RNA complementary to one entire strand-equivalent is transcribed. RNA made late in infection is very heterogeneous in length and a large fraction of it contains self-complementary sequences. Late genes are clustered near the central region of the genome. Vaccinia virus mRNAs do not appear to be synthesized by a splicing mechanism.

Phosphorylation in vivo of a vaccinia-virus structural protein found associated with the ribosomes from infected cells

When vaccinia-virus-infected cells were labeled with radioactive phosphate in the absence of viral gene expression an additional phosphoprotein, containing phosphoserine, was found specifically associated with the ribosomes. The phosphoprotein was removed from the ribosomes following a 0.5 M KCl washing or after EDTA treatment. This additional phosphoprotein was found in infected cells after either a long (3-4 h) or a short (30 min) labeling period; it was detected when the infected cells were incubated in the presence or absence of an inhibitor of RNA or protein synthesis. This phosphoprotein originated from the phosphorylation of vaccinia virion structural protein VP11b (Mr 11,000) at a specific site since only a single major phosphopeptide was obtained after trypsin digestion. This phosphoprotein was also present in purified vaccinia virions labeled with radioactive phosphate. VP11b protein was phosphorylated in vitro by the protein kinase associated with the cores. When the reaction was carried out at an alkaline pH the phosphorylation in vitro occurred at different sites in the protein; at neutral pH the phosphorylation of VP11b was more specific and, as judged by tryptic peptide analysis, occurred mainly at the same site as in the phosphorylation in vivo. A role for the involvement of phosphoprotein VP11b in the establishment of the shut off of host protein synthesis by vaccinia virus is suggested.

Multiple roles for ATP in the synthesis and processing of mRNA by vaccinia virus: specific inhibitory effects of adenosine (beta,gamma-imido) triphosphate

Adenosine (beta,gamma-imido)triphosphate (AMP-PNP) and guanosine (beta,gamma-imido)triphosphate (GMP-PNP) are analogs of ATP and GTP with non-hydrolyzable gamma-phosphates. Although both AMP-PNP and GMP-PNP were used in place of ATP and GTP by Escherichia coli RNA polymerase to transcribe vaccinia virus DNA, only GMP-PNP was used by the transcriptase present within vaccinia virus cores. AMP-PNP specifically prevented initiation of transcription, since RNA initiated in the presence of ATP, GTP, and CTP was subsequently elongated by incubating the washed cores in the presence of AMP-PNP, GTP, CTP, and UTP. The RNA formed in this manner, however, was (i) several times longer than normal transcripts, indicating a defect in chain termination and/or cleavage of nascent RNA, (ii) was not polyadenylylated (although free polyadenylic acid formed), and (iii) was not extruded from the virus cores. Nearest neighbor analysis demonstrated that AMP-PNP was incorporated adjacent to all four nucleotides, and hybridization to restriction endonuclease fragments of vaccinia virus DNA indicated that the high-molecular-weight RNA was transcribed from representative fractions of the entire genome. The possibility of a block in processing rather than or in addition to a block in chain termination was suggested by the cleavage of the high-molecular-weight RNA within the core after replacement of AMP-PNP with ATP. Cleavage of purified high-molecular-weight RNA by a soluble endoribonuclease extracted from vaccinia virus cores, however, was not dependent upon ATP, nor was it inhibited by AMP-PNP. The latter results suggest that AMP-PNP blocks a step preceding cleavage.

Analysis of the methylated 'cap' structures of vaccinia mRNA by two-dimensional thin-layer chromatography

Two different twodimensional cellulose thinlayer separations for blocked, methylated mRNA 5'-termini are described. They allow rapid analysis even of complex mixtures of mRNA "cap" structures on the basis of their methyl group content and base composition. These simple procedures are especially useful for the analysis of [3H-methyl]-labeled mRNA in combination with tritium fluorography. A qualitative and quantitative analysis of the methylated "cap" structures of in vitro labeled Vaccinia "core" mRNA is presented. The presence of methylated "cap" structures in Vaccinia RNA increases the in vitro translation efficiency of methylated Vaccinia RNA over Vaccinia RNA transcribed in the absence of a methyl group donor.

Heat inactivation of vaccinia virus particle-associated functions: properties of heated particles in vivo and in vitro

The heat inactivation characteristics of several vaccinia virus particle-associated functions known to be involved in the transcription of the genome were examined. All functions were more resistant to heat than infectivity. Noninfectious particles were generated which exhibited significant levels of activity of all enzymes examined, and their properties were investigaed both in vitro and in vivo. RNA was synthesized in vitro by such particles, although transport of the RNA into the surrounding medium was defective. This RNA was larger than that made in normal particles but it was polyadenylated and functioned in vitro as a message coding for normal early proteins. The sequences transcribed were similar to those transcribed in normal particles, and we suggest that the production of abnormally large RNA is due to a defect in transcriptional termination. We could not detect any virus-specific protein or RNA synthesis in cells exposed to these inactivated particles and conclude that the loss of infectivity caused by heating is due to a general decline in the activities of a number of particle functions.

Characteristics of a coupled cell-free transcription and translation system directed by vaccinia cores

1. A coupled transcription and translation system is described in which protein synthesis is directed by mRNA synthesised in situ by vaccinia virus cores. The cell-free system is based on a micrococcal-nuclease-treated reticulocyte lysate. 2. The polypeptides made in vitro include many authentic early vaccinia proteins, but also other proteins which were not detected in infected cells. 3. Concentrations of cores which inhibit host cell protein synthesis in vivo caused a delayed inhibition of translation in vitro; this was partly, but not entirely, due to dsRNA associated with the cores. 4. The mRNA made was methylated by core enzymes. Inhibition of methylation reduced the rate of translation tenfold; unmethylated RNA bound ribosomes poorly, but was nevertheless translated faithfully.

In vitro inhibition of protein synthesis by purified cores from vaccinia virus

The mechanism of the shutoff of cellular protein synthesis in vaccinia virus-infected cells has been investigated by using in vitro systems. Purified vaccinia cores cause inhibition of endogenous mRNA translation in nonpreincubated reticulocyte lysates and Ehrlich ascites tumor cell-free systems. Translation of viral mRNA from turnip yellow mosaic virus is also impaired in wheat germ cell-free extracts. The block induced by vaccinia cores in protein synthesis is not due to a decrease in the availability of mRNA but rather to an alteration of the cellular translational machinery. No nucleolytic activity able of digesting mRNA could be detected in purified vaccinia cores with three sensitive tests. There is a lack of inhibition in the poly(Phe)-poly(U) system, which bypasses the normal initiation process. An almost complete disaggregation of polyribosomes in the reticulocyte lysate appears when vaccinia cores are present. These results indicate that mRNA translation in a cell-free system is affected predominantly at the level of polypeptide chain initiation.

Inhibition of host protein synthesis in vaccinia virus-infected cells in the presence of cordycepin (3'-deoxyadenosine)

Cordycepin inhibited efficiently viral mRNA and polyadenylic acid syntheses in vaccinia virus-infected cells, but allowed the shutoff of host protein synthesis to occur. Therefore, cordycepin was used to study this shutoff in the absence of gene expression. Ribosome transit time was increased in infected cells, revealing an inhibition at the level of elongation and/or release of polypeptide chains. However, the disappearance of heavy polysomes in vaccinia virus-infected cells showed that the inhibition of host protein synthesis resulted predominantly from a block at the stage of initiation. This conclusion was confirmed by the recovery of heavy polyribosomes when low levels of cycloheximide were added to slow down ribosome release from the mRNA. Similar amounts of cellular mRNA (present in the polyribosomes) were found in vaccinia virus-infected cells and in mock-infected cels (exposed to cordycepin), showing that the cellular mRNA was not inactivated in these conditions. It was concluded that a component of the vaccinia virion inhibits, in the absence of viral RNA and polyadenylic acid syntheses, host protein synthesis at the level of initiation and, to a lesser extent, at the level of elongation (and/or release) of polypeptide chains.

5'-Terminal 7-methylguanosine and mRNA function: influence of potassium concentration on translation in vitro

Vaccinia mRNAs containing either 5'-terminal m7G or unmethylated 5'-terminal structures were synthesized in vitro and their relative efficiencies of translation were compared in wheat germ and reticulocyte cell-free protein-synthesizing systems. The importance of the m7G group for efficient translation increases as the K+ concentration is raised. At K+ concentrations optimal for translation of mRNA containing m7G, unmethylated mRNA is translated at the same relative low efficiency in both cell extracts. The rate of binding of mRNA to ribosomes at K+ concentrations close to those found in intact cells is strongly influenced by the presence of m7G regardless of the source of the cell extract.

Methyl group analysis of virion-associated high-molecular-weight RNA synthesized in vitro by purified vaccinia virus

The methylation pattern of virion-associated high-molecular-weight RNA synthesized in vitro by purified vaccinia virus has been determined. Analysis of purified high-molecular-weight RNA synthesized with S-[methyl-3H]-adenosylmethionine and alpha[32P]UTP as precursors gave the following results. (i) Eessentially all molecules contained blocked and methylated structures of the type m7G(5')ppp(5')Gm and m7G(5')ppp(5')Am. (ii) There was no detectable methylation at internal sites. (iii) Under several different conditions of synthesis, the ratio of molecules containing m7G(5')ppp(5')Gm to those containing m7G(5')ppp(5')Am was imilar for both the virion-associated high-molecular-weight RNA and the virion-released 8-12S mRNA.