Rescue at nonpermissive temperature of complementation group II temperature-sensitive mutants of vesicular stomatitis virus by uv-irradiated VSV

Nongenetic complementation in VSV: asymmetric contribution of the L proteins of each parent in the rescue of group I ts mutants

Complementation group I temperature-sensitive mutants of vesicular stomatitis virus (VSV) are rescued at nonpermissive temperature by UV-irradiated virus. Rescue is a nongenetic process mediated by the structural L protein molecules of the parental irradiated virus. This is shown by action spectra analysis (V. Deutsch, B. Muel, and G. Brun (1977), Virology 77, 294-305), efficiency of rescue at doses high enough to inactivate every gene I, and rescue by irradiated defective-interfering short particles. Viral molecular synthesis at 39.6 degrees using the ts genomes as templates and stimulated by UV-irradiated virus is shown by gel electrophoresis of rescued virion proteins. Parental strain ts 053(I) is thermolabile in vitro while the thermostability of the rescued virions, genetically characterized as ts group I virus, is identical to that of helper wt or ts+ revertant. This suggests that some parental Lwt molecules are reincorporated in the rescued virions, together with newly synthesized Lts molecules. Efficiency variation of the rescue as a function of the multiplicity of infection of the UV-irradiated virions depends on the m.o.i. of the unirradiated ts I mutants. This result suggests that rescue depends on the concentration of the helper L molecules and also of that of the L initially bound to the ts template. That L of both parents contribute to rescue is supported by the observations that (1) rescue by UV-wt is strongly diminished after in vitro heating of thermolabile ts O53(I). (2) Intragenic rescue can be demonstrated: The helper activity of a given UV-ts I mutant is different according to the unirradiated ts I mutant used; the activity of helper L associated with different templates in intragenic heterologous combinations is higher or lower than its activity in the homologous combination (self-rescue control), instead of being equal as expected. (3) Efficiency of rescue by UV-wt also varies according to the ts I mutant. The initially bound Lts seems therefore to play a role important and different from that of the helper L. Contribution of both parent L to rescue seems thus to be qualitatively different.

UV irradiation analysis of complementation between, and replication of, RNA-negative temperature-sensitive mutants of Newcastle disease virus

Random UV irradiation-induced lesions destroy the infectivity of Newcastle disease virus (NDV) by blocking downstream transcription from the single viral promoter. The nucleocapsid-associated polypeptides most likely to be involved in RNA synthesis are located at the extreme ends of the genome: NP and P are promoter proximal genes, and L is the most distal gene. We attempted to order the two temperature-sensitive (ts) RNA-negative (RNA-) mutant groups of NDV by determining the UV target sizes for the complementing abilities of mutants A1 and E1. After UV irradiation, E1 was unable to complement A1, a result compatible with the A mutation lying in the L gene. In contrast, after UV irradiation, A1 was able to complement E1 for both virus production and viral protein synthesis, with a target size most consistent with the E mutation lying in the P gene. UV-irradiated virus was unable to replicate as indicated by its absence in the yields of multiply infected cells, either as infectious virus or as particles with complementing activity. After irradiation, ts mutant B1 delta P, with a non-ts mutation affecting the electrophoretic mobility of the P protein, complemented E1 in a manner similar to A1, but it did not amplify the expression of delta P in infected cells. This too is consistent with irradiated virus being unable to replicate despite the presence of the components needed for replication of E1. At high UV doses, A1 was able to complement E1 in a different, UV-resistant manner, probably by direct donation of input polypeptides. Multiplicity reactivation has previously been observed at high-multiplicity infection by UV-irradiation paramyxoviruses. In this case, virions which are noninfectious because they lack a protein component may be activated by a protein from irradiation virions.