Studies on the control of the genes for transcription and translation in Escherichia coli K12 I. tufB and rplA, K have separate promoters

Relative activities of the transcriptional regulatory sites in the rplKAJLrpoBC gene cluster of Escherichia coli

The pattern of transcription of the rplKAJLrpoBC gene cluster of Escherichia coli appears to be complex. At least four different promoters and a transcriptional attenuator have been identified. To compare the relative effect of each of the putative promoters and the attenuator on transcription of these genes, we fused these regulatory sites to lacZ. These transcriptional fusions were constructed on lambda transducing phages so a single copy of each could be stably integrated into the chromosome. The level of beta-galactosidase in a lysogen of each phage reflects the activity of the transcriptional regulatory site. We find that the promoters preceding rplK (rplKp) and rplJ (rplJp) are indeed the major promoters of this gene cluster. The minor promoter before rplL (rplLp) is much weaker and contributes little to the transcription of the downstream genes. Under these conditions, we find no evidence of a promoter (rpoBp) in the rplL-rpoB intercistronic region. The attenuator (atn) terminates ca. 70% of the transcripts initiated at the promoters preceding it. Although we cannot rule out that some transcripts from rplKp may read through into rplJLrpoBC, we find that rplJp alone is sufficient for high-level expression of these genes.

Insertions of transposon Tn5 into ribosomal protein PNA polymerase operons

The genetic organization and interrelationships between the two ribosomal protein transcription units (the L11 and L10 operons) from near 89 min on the Escherichia coli chromosome were studied by using insertional mutations generated by the kanamycin-resistant transposable element Tn5. The polar effects of Tn5 insertions on the expression of the L11, L1, L10, and L12 ribosomal protein genes and the beta RNA polymerase subunit gene were examined (i) by the level of beta-galactosidase activity generated from L10-lacZ and beta-lacZ gene fusions, (ii) by direct sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the proteins specified by plasmid ribosomal protein genes in UV-irradiated maxicells, and (iii) by urea-polyacrylamide gel electrophoresis of plasmid- and chromosome-specified L12 protein. The results confirmed the organization of these genes into two transcription units as follows: PL11, rplK (L11), rplA (L1), PL10, rplJ (L10), rplL (L12), rpoB (beta). . .; they also localized the position of the PL10 promoter within an 80-nucleotide region near the end of the L1 gene. The results also support the idea that the translational regulatory proteins for the L11 and L10 operons are L1 and L10, respectively, and that the expression of the L12 gene is closely linked to L10 gene expression.

Oversynthesis of elongation factors G and Tu in Escherichia coli

We induced the oversynthesis of elongation factors Tu and G by using multicopy plasmids carrying the structural genes for these proteins under the control of the lac operator-promoter. We found no evidence that accumulation of excess elongation factor Tu or G affects the expression of genes for ribosomal proteins or elongation factors.

Regulation of the synthesis of E. coli elongation factor Tu

Rapidly growing E. coli with two active genes (tufA, tufB) for elongation factor (EF) Tu contains three times as much EF-Tu (tuf) mRNA as EF-G (fus) mRNA on a molar basis, but about seven times as much EF-Tu as EF-G or ribosomes. The concentration and translational efficiency of fus (EF-G) mRNA is about that for ribosomal protein mRNAs. The high molar concentration of EF-Tu relative to EF-G or ribosomes is achieved in part by translating tuf mRNA more efficiently than these other mRNAs. In a tufA+ tufB-: : Mu strain, the tuf:fus mRNA ratio is 1, but the concentration of EF-Tu and tuf mRNA is the same as in the wild-type strain. Thus cells with only an active tufA gene increase the concentration but not the translational efficiency of tuf mRNA. In such cells the concentration of fus mRNA is almost three times that in the wild-type strain. Because the tufA gene is distal to but cotranscribed with the fus gene as part of the four gene str operon, the wild-type concentration of tuf mRNA in these tufB- cells must be produced by increasing the concentration of transcript corresponding to the entire str operon. Thus transcription of the tufA gene can only proceed from the str promoter. Extracts of the tufB- cells contain tuf transcripts that correspond not only in size to the entire 4.5 kb str operon, but also to the size (approximately 1 kb) of a tuf gene. Our evidence suggests that this 1 kb tuf transcript is derived by posttranscriptional modification of the primary str operon transcript and that this modification could in part explain the high translational efficiency of tuf mRNA.

Characterization of promoter-cloning plasmids: analysis of operon structure in the rif region of Escherichia coli and isolation of an enhanced internal promoter mutant

Using the promotor-cloning vehicle described by An and Friesen (J. Bacteriol. 140:400-410, 1979), Escherichia coli chromosomal deoxyribonucleic acid fragments derived from the lambda drifd18 transducing phage were cloned in one of several unique restriction endonuclease sites adjacent to tetracycline(tet) genes that lack their own promotor. One of these plasmids has been used to isolate nine variants having mutations that lie in a putative internal promoter which is located between rplL and rpoB. Deoxyribonucleic acid sequence analysis revealed that, in all nine mutants, a single base change, C to T, in the ribonucleic acid polymerase recognition site led to a large increase in promoter activity. Analysis of a variety of plasmids in which tet is fused to various promoters yielded the following results: (i) rplK and rplA, genes for ribosomal protein L11 and L1, respectively, were cotranscribed from a common promoter located upstream from rplK; (ii) there was a strong promoter in the region between the rplKA operon and rplJ, the gene for ribosomal protein L10; (iii) an attenuator region was located between rplL, the gene for ribosomal protein L12, and rpoB, the gene for ribonucleic acid polymerase subunit beta; (iv) transcription terminated immediately after rpoC, the gene for ribonucleic acid polymerase subunit beta'; (v) a gene coding for unknown protein U, which is located between tufB and the rplKA operon, had its own promoter; (vi) the tufB gene was separated from all of the genes described above and had its own promoter.

Characterisation of a lambda transducing phage carrying the F conjugation gene traG

A lambda transducing phage carrying the traGSTD genes of the E. coli K12 factor F was isolated by an in vivo technique, and characterized in tra complementation tests, by determining its restriction endonuclease fragment sizes, and by measuring heteroduplex molecules. The size and location on the F physical map of the tra transducing segment was thereby determined. Comparison of the proteins synthesized in UV-irradiated cells by this phage and by a derivative carrying the amber traG79 mutation, allowed the traG product to be identified as a protein of molecular weight 100,000. In the same experiments, the sizes of the traT and traD products made by the phage were also measured, being 25,000 and 85,000 daltons respectively.