Identification of two copies of the gene for the elongation factor EF-Tu in E. coli

Analysis of the proteins synthesized in ultraviolet light-irradiated Escherichia coli following infection with the bacteriophages lambdadrifd 18 and lambdadfus-3

The presence of EF-Tu, RNA polymerase subunit alpha, and EF-G on the lambdadfus-3 genome and EF-Tu, ribosomal proteins L7/L12, and RNA polymerase subunit beta on the lambdadrifd 18 genome has been confirmed using a two-dimensional gel electrophoresis technique sensitive to changes in isoelectric point and molecular weight. In this system two EF-Tu gene products could not be resolved. Following infection of ultraviolet light-irradiated Escherichia coli with either lambdadfus-3 or lambdadrifd18, the EF-Tu gene, tufA, near 65 minutes on the genetic map is expressed as 3-4 copies per EF-G molecule. The EF-Tu gene, tufB, near 79 minutes on the genetic map, is expressed at about one-third of this rate. alpha is expressed as 1 copy per EF-G molecule, beta as 0.14 per EF-G molecule and L7/L12 as 2.5 per EF-G. These figures compare well with the relative amounts found in exponentially-growing cells, in which the ratio of EF-Tu to EF-G is approximately 5. Almost 90% of the total number of proteins (calculated on a molecular weight basis) which theoretically can be encoded on the lambdadrifd18 have been identified on the two-dimensional gel.

Deletions of ribosomal protein genes in Escherichia coli merodiploids heterozygous for resistance to streptomycin and spectinomycin

In a merodiploid strain of Escherichia coli heterozygous for the ribosomal protein genes spc and str, deletions were observed preventing the expression of either gene but permitting the expression of the other. This suggests that the spc and str genes are in separate transcriptional units.

A relaxed mutant with an altered ribosomal protein L11

Relaxed mutants of Escherichia coli have been isolated which have an altered electrophoretic mobility of ribosomal protein L11. It can be shown that reversion to stringency in one of these mutants occurs simultaneously with a reversion of L11 protein to tis normal mobility. The L11 structural gene, rplK, maping near rif, is carried by the bacteriophage lambdacI857S7drifd18, and is most likely identical with relC.

Synthesis of ribosomal RNA in E. coli: analysis using deletion mutants of a lambda transducing phage carrying ribosomal RNA genes

Transducing phage lambdarifd18 carries on rRNA transcription unit containing genes for 5S, 16S, and 23S rNAs and also tRNAGlu/2. Mutants were isolated from this phage that carry deletions removing various amounts of the distal end of this transcription unit. These deletions were physically mapped on the lambdarifd18 phage genome. Synthesis of rRNAs and of tRNAGlu/2 was examined in ultraviolet-irradiated E. coli cells infected with lambdarifd18 or with various deletion mutants. It was observed that mutant phages in which the distal end (the 5S rRNA gene and a part of the 23S rRNA gene) of the rRNA transcription unit is deleted can still synthesize both 16S rRNA (or its precursor) and tRNAGlu/2. Apparently, the post-transcriptional cleavage that produces these RNA molecules does not require the presence of the entire transcription unit, that is, it can take place without the complete structure of the transcript ("30S pre-ribosomal RNA"). In addition, the experimental results support the gene order, 16S rRNAGlu/2, 23S rRNA, and 5S rRNA genes, in the rRNA transcription unit carried by lambdarifd18.

Transfer RNA genes between 16S and 23S rRNA genes in rRNA transcription units of E. coli

We have identified genes for tRNAGLU/2 on the transducing phages o80d3ilvsu7+ (see Ohtsubo et al., 1974) and lambdarifd18 (Kirschbaum and Konrad, 1973), and a gene for tRNAlle/1 on the transducing phage o80rifr (Konrad, Kirschbaum, and Austin, 1973). All these phages have previously been shown to carry genes for rRNA (Ohtsubo et al., 1974; Lindahl et al., 1975; Jaskunas et al., 1975a). We have analyzed the position of these tRNA genes by hybridizing purified RNAs to restriction fragments of the phage DNA. The tRNA genes are located inside the rRNA transcription unit in the spacer region between the 16S and 23S rRNA genes.

Identification of a gene for the alpha-subunit of RNA polymerase at the str-spc region of the Escherichia coli chromosome

A structural gene for the alpha-subunit of RNA polymerase (nucleosidetriphosphate:RNA nucleotidyltransferase; EC 2.7.7.6) has been identified and mapped between spcA and trkA, near 64 min on the E. coli chromosome. It appears to be coordinately expressed and possibly cotranscribed with the genes for ribosomal proteins S11, S4, and L17.

Content of elongation factor Tu in Escherichia coli

The content of elongation factor Tu in E. coli B has been determined both by radioimmune assay and by GDP binding. The two assays gave comparable results: cells growing at 2 doublings per hour contained about 8 molecules of Tu per ribosome, whereas those growing at 0.22 doublings per hour contained about 14 molecules per ribosome. These levels resemble those reported for tRNA, in contrast with the 1:1 ratio of factor to ribosomes reported for elongation factors Ts and G.