Characterization of the mutations responsible for the electrophoretic mobility differences in the NS proteins of vesicular stomatitis virus New Jersey complementation group E mutants.

Temperature-sensitive (ts) mutants of vesicular stomatitis virus, New Jersey serotype, classified in complementation group E contain lesions in the NS gene, which manifest as marked electrophoretic mobility differences of the mutant NS proteins in SDS-polyacrylamide gels. We have cloned full-length cDNA copies of the mutant NS mRNAs, and have determined their nucleotide sequences. tsE1 and tsE3 had single nucleotide changes, and tsE2 had two nucleotide changes, compared to the wild-type NS gene. Three of the mutations were clustered in a region of 18 nucleotides. All the nucleotide differences resulted in amino acid substitutions, which in each case changed the charge of the amino acid concerned. Analysis of the wild-type and mutant NS protein sequences by the method of Chou & Fasman indicated that single amino acid substitutions can radically alter the predicted secondary structure, and these data are discussed in relation to the observed electrophoretic mobility differences.

Temperature sensitivity of the transcriptase of mutants tsB1 and tsF1 of vesicular stomatitis virus New Jersey is a consequence of mutation affecting polypeptide L.

Two conditional transcriptase-negative mutants of vesicular stomatitis virus (VSV) serotype New Jersey, tsB1 and tsF1, their revertants tsB1/R1 and tsF1/R1 and the wildtype virus were dissociated into pellet, NS and L fractions and, after reconstitution of these in various combinations, the transcriptase activities were assayed in vitro at the permissive (31 degrees C) and restrictive (39 degrees C) temperatures. The pellet fractions contained the virion RNA-polypeptide N complexes, while the NS and L fractions were essentially pure preparations of these polypeptides. The synthesis of RNA by the reconstituted pellet and L fractions was inhibited at 39 degrees C only when the L fractions of tsB1 or tsF1 were used. Addition of the NS fractions to the reconstituted pellet and L fractions did not alter the rates of RNA synthesis. These results demonstrate that polypeptide L is the temperature-sensitive polypeptide of both mutants tsB1 and tsF1 and support previous observations that polypeptide L is the transcriptase itself. The fact that a second mutant of complementation group F, tsF2, is transcriptase-positive but replicase-negative suggests that polypeptide L is involved both in transcription and replication. Intracistronic complementations may account for the observation that the temperature-sensitive mutations affect polypeptide L in complementation groups B and F.

The role of polypeptides L and NS in the transcription process of vesicular stomatitis virus New Jersey using the temperature-sensitive mutant tsE1.

The roles of the L and NS polypeptides in transcription by vesicular stomatitis virus New Jersey were studied using a mutant, tsE1, which contains a temperature-sensitive transcriptase and an altered NS polypeptide, both phenotypic changes being the consequence of the ts mutation. Mutant tsE1, its revertant (tsE1/R1) and the wild-type virus were dissociated into sub-viral fractions and, after reconstitution of these fractions in all combinations, the transcriptase was assayed in vitro at the permissive (31 degrees C) and restrictive (39 degrees C) temperatures. Reconstitution of the pellet fractions (containing polypeptide N complexed with the virion RNA) and the supernatant fractions (containing polypeptides L and NS) restored transcriptase activity at 31 degrees C in all combinations, but at 39 degrees C transcription was observed only in the presence of the supernatant fractions of wild-type and revertant viruses but not in the presence of the supernatant fractions of tsE1. When the pellet fractions and the L fractions were reconstituted, the transcriptase activity was restored in all combinations both at 31 degrees C and 39 degrees C. However, in vitro transcription at 39 degrees C by reconstituted pellet and L fractions was strongly inhibited when the NS fraction of tsE1 was also added, while addition of the NS fractions of wild-type and revertant viruses had no effect. Since only traces of polypeptide NS were present in the L fractions and none in the pellet fractions, the results strongly suggest that polypeptide L is the transcriptase itself while polypeptide NS exerts some control over transcription.

Biochemical characterization of the tsE1 mutant of vesicular stomatitis virus (New Jersey). Alterations in the NS protein.

Alterations in the NS protein of the tsE1 mutant of vesicular stomatitis virus (New Jersey serotype) appear to be responsible for its temperature-sensitive phenotype. The NS proteins of thermostable revertants of tsE1 migrated in polyacrylamide gels containing sodium dodecyl sulfate with apparent sizes which were identical to tsE1 NS, or which were 5% or 14% larger than tsE1 NS. These novel differences persisted during electrophoresis in 10% and 12.5% acrylamide gels, and in gels with gradients of acrylamide, suggesting that aberrant sodium dodecyl sulfate binding was not involved. Co-infection of cells with pairs of viruses resulted in the synthesis of both types of NS protein, suggesting that no trans-acting phenomenon was involved. Two-dimensional gel electrophoresis demonstrated that each of the NS proteins consisted of several species, but the isoelectric points of the proteins from different viruses overlapped. Furthermore, all of the NS species from a particular virus migrated with the same apparent molecular weight, suggesting that aberrant phosphorylation was not responsible for the apparent differences in size. Finally, tryptic peptide maps of amino acid and 32Pi-labeled NS proteins demonstrated that the revertant NS proteins contained all of the peptides and phosphopeptides of tsE1 NS, but each revertant NS with an apparently larger protein also contained an extra nonphosphorylated peptide. These data are consistent with the idea that the reversion of the temperature-sensitive phenotype of tsE1 can be accompanied by production of a significantly larger NS protein.

Temperature-sensitive mutants of complementation group E of vesicular stomatitis virus New Jersey serotype possess altered NS polypeptides.

In vesicular stomatitis virus New Jersey serotype polyacrylamide gel electrophoresis was unable to distinguish the polypeptides of the temperature-sensitive (ts) mutants of complementation groups A, B, C, and F from those of the wild-type virus. However, the NS polypeptide of the representative mutant of group E, ts E1, had a significantly greater electrophoretic mobility than that of the wild-type virus NS polypeptide. The electrophoretic mobilities of the NS polypeptides of the three mutants of complementation group E varied, being greatest in the case of ts E1, slightly less for ts E2, and only a little greater than that of wild-type virus NS polypeptide in the case of ts E3. Since the NS polypeptides of the revertant clones ts E1/R1 and ts E3/R1 have mobilities identical to that of wild-type NS polypeptide, the observed altered mobilities of the group E mutants are almost certainly the direct result of the ts mutations in the E locus. The electrophoretic mobilities of the intracellular NS polypeptides of the group E mutants were indistinguishable from those of their virion NS polypeptides. The electrophoretic mobilities of the NS polypeptides of the group E mutants synthesized in vitro using mRNA synthesized in vitro by TNP were identical to those of the NS polypeptides of their purified virions. The NS polypeptides of all three mutants were labeled with (32)P(i) to approximately the same extent as wild-type virus NS polypeptide, indicating that gross differences in phosphorylation of this polypeptide are unlikely to account for the altered mobilities. We propose a model in which the NS polypeptide consists of at least three loops held in this configuration by hydrophobic or ionic forces or both and stabilized by phosphodiester bridges. If a mutation affects one of the amino acids to which the phosphate is covalently linked, the phosphodiester bridge cannot be formed, and, as a result, in the presence of sodium dodecyl sulfate the affected loop opens and thus the NS polypeptide migrates further into the gel. Such a configuration may also explain the multifunctional nature of the NS polypeptide.

Proposed replicative role of the NS polypeptide of vesicular stomatitis virus: structural analysis of an electrophoretic variant.

The structural lesion in the temperature-sensitive mutant E1 of the New Jersey serotype of vesicular stomatitis virus has been assigned to the NS protein. Although the packaged wild-type and mutant NS proteins were similarly phosphorylated, the mutant NS protein migrated faster than the wild-type NS protein in polyacrylamide slab gels electrophoresed in the presence of sodium dodecyl sulfate. The resolution appears to be the result of conformational rather than size differences since the two proteins comigrated in polyacrylamide gels which contained 4 M urea in addition to sodium dodecyl sulfate. Peptide maps, obtained by limited proteolysis of 32P-labeled wild-type and mutant NS proteins with Staphylococcus aureus V8 protease and papain, revealed striking differences which suggested that the mutant alteration could involve an aspartic or glutamic acid residue. Since NS proteins obtained from naturally occurring revertants of E1 were indistinguishable from the wild-type protein in all of these analyses, the structural alteration in the mutant NS protein correlates with the functional lesion. Because E1 is defective in the RNA replication pathway at the restrictive temperature, a replicative role is proposed for the NS protein.

Physical properties of New Jersey serotype of vesicular stomatitis virus and its defective particles.

The wild-type New Jersey serotype of vesicular stomatitis virus generated two types of defective interfering T-particles. The physical properties of these particles and the wild-type virion were determined by laser light scattering spectroscopy, sedimentation measurements, and electron microscopy.