J. Mol. Biol. (1977) 109, 23-47 Mapping of a Cluster of Genes for Components of the Transcriptional and Translational Machineries of Escherichia colit LASSE LINDAHL, ]~-ASAYUKI ~rAMAMOTO,M.&SAYASU NOMURA Institute for Enzyme Research, Departments of Genetics and Biochemistry University of Wisconsin, Madison, Wise. 53706, U.S.A. JOEL B. KIRSCHBAUM, BERNARD ALLET AND JEAN-DAvID ROCHAIX D~partement de Biologic Mol~culaire, Universit~ de Gen~ve 30 quai Ernest-Ansermet, CH-1211, Gen~ve 4, Switzerland (Received 9 March 1976) A number of genes that code for components of translational machinery are closely linked to the genes for the RNA polymerase subunits fl and fl' and are carried by a transducing phage, Arifd18. In order to map these genes, we have first investigated the physical structures of hr/fdl8 and the related, but indepen- dently isolated, transducing phage, )~r/fd12, using DNA heteroduplex analysis and digestion with various restriction enzymes. The order of the protein genes was determined by isolation of the DNA restriction fragments and examination of their ability to stimulate synthesis of proteins in vitro. From these experiments and from the results on the RNA gene mapping reported previously (Lund et al., 1976), the following order lhas been deduced: genes for 16 S rRNA, tRNA.(, ~lu (gltT), 23 S rRNA, 5 S rRNA, translational elongation factor Tu (tu]B), ribosomal proteins L1 and L11 (rpIA and rplK, order not determined), ribosomal protein L7/L12 (rplL), RNA polymerase subunit fi (rpoB), and RNA polymerase sublmit fi' (rpoC). From heteroduplex analyses of the three independently isolated transducing phages, Zrifdl2, hr/fd18, and r we conclude that the gene order identified on hripl8 is probably identical to that on the Escherichia coli chromosome, except that the identity of the tRNA gene in the rRNA trans- cription unit is ambiguous. 1. Introduction Regulation of synthesis of many components of the transcriptional and translational machineries seems to be instrumental in the adaptation of bacterial cells to their chemical environment (for a review, see e.g. Kjeldgaard & Gausing, 1974). The under- standing of this regulation depends not only on the identification of possible regulatory elements, but also on the elucidation of the organization of the large number of genes coding for these components. Many of these genes have been localized in the str-spe region at about 72 minutes This is paper number 1955 from the Laboratory of Genetics. 23