Streptomycin resistant Escherichia coli mutant temperature sensitive for the production of Qβ infective particles

A streptomycin resistant Escherichia coli mutant has been isolated that is temperature sensitive for Qβ phage, but not for the group I RNA phages f2, MS2, and R17. The growth of Qβ in the mutant at the nonpermissive temperature (42°C) results in the release of a near normal burst of noninfectious particles that cosediment with Qβ in a sucrose gradient. It is assumed that the mutant is defective at elevated temperatures in the suppression of nonsense codons, thereby producing Qβ like particles which are noninfectious because of the lack of the read through protein A₁.