Organization of ribosomal protein genes in Escherichia coli: I. Physical structure of DNA from transducing λ phages carrying genes from the aroE-str region

The physical structures of the genomes of five transducing bacteriophages (λaroE, λtrkA, λspc1, λspc2, and λfus2) carrying various portions of the aroE-trkA-spc-str segment of the Escherichia coli chromosome have been determined. Two methods were used: (a) heteroduplex analysis of DNA molecules from these phages, and (b) analysis of fragments obtained from digestion of the DNA by restriction endonucleases EcoRI and HindIII. In λaroE, λtrkA, λspc1 and λspc2, whose genome lengths vary from about 75% to about 104% of the λpapa genome, the right arm of λ DNA is present, whereas various portions of the left arm have been replaced by E. coli DNA. In λfus2, however, about 93% of the λ DNA molecule is replaced by E. coli DNA, the resultant genome being 103.5 %λ units long (Figs 1 and 2). All five phages contain an identical λ-E. coli junction at 1.9 %λ units from the left λ terminus, and there is complete homology between the common portions of the inserted E. coli DNA. Since these phages were independently isolated, we believe that the genetic organization of the E. coli DNA carried by these phages probably reflects the organization of the relevant segments of the E. coli chromosome. Comparison of the physical and genetic maps of these transducing phages has allowed us to assign a physical position to the ribosomal and neighbouring genes, including those coding for the α subunit of RNA polymerase and the elongation factors G and Tu, on the bacterial DNA.