Behaviour of ts mutants of pseudorabies virus in the range between permissive and nonpermissive temperature

The growth properties of pseudorabies virus (PRV) strain V BUK, wild type and its four ts mutants, were examined using highly accurate temperature measurements in the incubator and on the cell sheet. The transition from permissive to nonpermissive temperature occurred within an interval of 1 degree C. The midpoint of this interval was termed the semipermissive temperature since at this temperature the reproduction and consequently the plaquing of mutant viruses was not completely restricted. The "leakiness" of ts mutants might be due to their incubation at semipermissive temperature. Under semipermissive conditions and at high virus inputs, three mutants exhibited nearly complete inhibition of plaquing. In an experimental mixture of to mutants and PRV-BUK wild type, the latter was not affected by the inhibition. This might be due to an enhanced sensitivity of the mutants, but not of the wild type, to interferon under these conditions.