Growth and Maturation of a Vesicular Stomatitis Virus Temperature-Sensitive Mutant and Its Central Nervous System Isolate †

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A temperature-sensitive (ts) mutant of vesicular stomatitis virus (VSV), tsG31, produces a prolonged central nervous system disease in mice with pathological features similar to those of slow viral diseases. tsG31 and the subsequent virus recovered from the central nervous system (tsG31BP) of mice infected with tsG31 were compared with the parental wild-type (WT) VSV for plaque morphology, growth kinetics, thermal sensitivity of the virions, and viral protein synthesis and maturation. Several properties of the central nervous system isolate distinguished this virus from the original tsG31 and the WT VSV. The WT VSV produced clear plaques with complete cell lysis, and the tsG31 produced diffuse plaques and incomplete cell lysis, whereas the tsG31BP had clear plaques similar to those of the WT VSV. Although plaque morphology suggested that tsG31BP virus was a revertant to the WT, growth kinetics in either BHK-21 or neuroblastoma (N-18) cells indicated that this virus was similar to tsG31, with a productive cycle at 31°C and no infectious virus at 39°C. At 37°C, however, the tsG31BP matured much slower than did the original tsG31 (and produced only 1% of the yield measured at 31°C). WT VSV produced similar quantities of infectious virions at 31, 37, and 39°C. The lack of infectious virions at 39°C for the ts mutants was presumably not due to a greater rate of inactivation at 39°C. Unlike WT VSV, which synthesized viral proteins equally well at all three temperatures, tsG31 had a reduced synthesis of all the structural proteins at 37 and 39°C, compared with that at 31°C; the formation of the M protein was most temperature sensitive. In addition, fractionation of the infected cells indicated that the incorporation of the M and N proteins into the cellular membranes was also disrupted at the higher, nonpermissive temperatures. Several characteristics of protein synthesis during tsG31BP infection at 39°C distinguished this virus from tsG31: (i) no mature viral proteins were detected at 39°C; (ii) several host proteins were [ill], suggesting that the virus was incapable of completely depressing host macromolecular synthesis; and (iii) a great proportion of the incorporated radioactivity was found in unusually high-molecular-weight proteins. In addition, at 37°C, the tsG31BP virus showed a decreased synthesis of viral proteins and reduced assembly of the viral structural proteins.

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