Unusual suppression properties of lysogens containing derivatives of ϕ80 psu3+

Nonsense codon suppressing lysogens of E. coli have been made using φ{symbol}80 psu₃⁺-A2 and φ{symbol}80 psu_oc⁺-A2, heat-sensitive amber and ochre suppressing derivatives, respectively, of bacteriophage φ{symbol}80. The various lysogens selected differ in strength of suppression as well as in heat sensitivity of suppressor function. Heat-resistant derivatives, some still carrying the A2 mutation, can be selected from the heat sensitive parents. Mapping expreiments indicate that the φ{symbol}80 derivatives integrate at the tyrTV locus, which contains two copies of tRNA₁^Tyr. The origin of the various suppressor phenotypes appears to be related to the great variety of distinctive recombination events possible either between the incoming tRNA₁^Tyrgene and the host copies, or among the three copies of this gene in the lysogens.