A specialized transducing lambda phage carrying the Escherichia coli genes for phenylalanyl-tRNA synthetase

A lambda phage has been isolated which specifically transduces the Escherichia coli pheS and pheT genes coding for the alpha and beta subunits of the phenylalanyl-tRNA synthetase (PRS). This phage transduces with high frequency (i) several temperature-sensitive PRS mutants to thermoresistance and (ii) a p-fluorophenylalanine resistant PRS mutant to sensitivity against this amino-acid analog. The in vitro PRS activities of such lysogens suggest that the alpha and beta subunits coded by the transducing phage complement the mutant host PRS-subunits in vivo by means of formation of hybrid enzymes. The transducing lambda phages were also used to infect UV light irradiated cells. The SDS-gel electrophoretic analysis of the proteins synthesized in such cells revealed that the phage codes at least for four different E. coli proteins. Two proteins with molecular weights of 94,000 and 38,000 daltons cross-reacted with an anti PRS serum and were thus identified as the beta and alpha subunits of PRS, respectively. A third protein with a molecular weight of 22,000 daltons is identical with the ribosomal initiation factor IF3 (Springer et al., 1977b). The other protein (Mr 78,000) is still unidentified.