Effects of altered rho gene product on the expression of the Escherichia coli histidine operon

Mastering the control of the Rho transcription factor for biotechnological applications

The present review represents an update on the fundamental role played by the Rho factor, which facilitates the process of Rho-dependent transcription termination in the prokaryotic world; it also provides a summary of relevant mutations in the Rho factor and the insights they provide into the functions carried out by this protein. Furthermore, a section is dedicated to the putative future use of Rho (the 'taming' of Rho) to facilitate biotechnological processes and adapt them to different technological contexts. Novel bacterial strains can be designed, containing mutations in the rho gene, that are better suited for different biotechnological applications. This process can obtain novel microbial strains that are adapted to lower temperatures of fermentation, shorter production times, exhibit better nutrient utilization, or display other traits that are beneficial in productive Biotechnology. Additional important issues reviewed here include epistasis, the design of TATA boxes, the role of small RNAs, and the manipulation of clathrin-mediated endocytosis, by some pathogenic bacteria, to invade eukaryotic cells. KEY POINTS: • It is postulated that controlling the action of the prokaryotic Rho factor could generate major biotechnological improvements, such as an increase in bacterial productivity or a reduction of the microbial-specific growth rate. • The review also evaluates the putative impact of epistatic mechanisms on Biotechnology, both as possible responsible for unexpected failures in gene cloning and more important for the genesis of new strains for biotechnological applications • The use of clathrin-coated vesicles by intracellular bacterial microorganisms is included too and proposed as a putative delivery mechanism, for drugs and vaccines.

Analysis and comparison of the internal promoter, pE, of the ilvGMEDA operons from Escherichia coli K-12 and Salmonella typhimurium

It was previously determined that the distal portion of the ilvGMEDA operon was expressed despite the insertion of transposons into ilvG and ilvE. This observation suggested the existence of internal promoters upstream of ilvE (pE) and ilvD (pD). The internal promoter pE, responsible for part of ilvEDA expression, has been analyzed both in vivo and in vitro. Our results indicate that: pE exists in both E. coli K-12 and S. typhimurium; pE is located in the distal end of the ilvM coding sequence; the pE sequence is highly conserved in the two bacteria; the amino acid sequence of the ilvM gene product is 93% homologous between the two bacteria; transcription from pE can be demonstrated both in vivo and in vitro; the efficiency of pE is essentially equivalent in the two bacteria.

DNA sequence changes of mutations in the histidine operon control region that decrease attenuation

The DNA sequence changes of 18 (9 different) mutations in the control region of the histidine operon of Salmonella typhimurium are presented. All of these mutations increase the level of expression of the operon, presumably by decreasing transcription termination at the attenuator. Five of the mutations were previously isolated hisO mutations, and the other four were isolated here as His+ pseudorevertants of His- stop codon mutations in the leader peptide gene. Only two mutations, O1242 and O3154, directly affect the terminator stem of the leader RNA. One mutation, O1202, creates a strong new stem that would compete with the terminator stem. Most of the other mutations damage other RNA stems. Their effect can best be explained by, and they thus provide supporting evidence for, the prevailing model of attenuator regulation involving alternative, competing RNA stems in the leader RNA. Two mutations that do not appear to significantly affect an RNA stem directly, including a deletion of three of the seven consecutive histidine codons, are best explained as effects of a translating ribosome upon the RNA stem structures, even though the histidine codons are not translated in the pseudorevertants.

Cloning and expression of the distal portion of the histidine operon of Escherichia coli K-12

The operator-distal genes hisBHAFI(E) of the Escherichia coli K-12 histidine operon were mapped on a DNA fragment 4,500 base pairs long. This fragment, originally present in a lambda transducing phage, was cloned in the vector plasmid pBR313. A restriction map was determined, allowing identification of the orientation of the genes in the fragment. The cloned genes were expressed in appropriate hosts, independent of the orientation of the DNA fragment, as shown by transformation tests and by enzyme assays of one of the gene products, hisB, histidinol phosphatase. An internal transcription initiation site was identified by isolation of the cellular RNA, hybridization to specific DNA probes, and mapping by S1 nuclease.

Genetic analysis of a temperature-sensitive Salmonella typhimurium rho mutant with an altered rho-associated polycytidylate-dependent adenosine triphosphatase activity

A conditional-lethal rho mutant of Salmonella typhimurium LT2 has been isolated. The mutation was selected as a suppressor of the polarity of an insertion sequence (IS)2-induced mutation (gal3) carried on an F' plasmid. In addition to suppression of IS2-induced polarity, the rho-111 mutation suppressed nonsense and frameshift polarity. The rho-associated polycytidylic acid-dependent adenosine triphosphatase activity in the mutant strain was elevated 15-fold above that in the parental strain, and the mutant rho protein was thermally unstable. A temperature-resistant revertant of the mutant strain did not suppress polarity and contained normal levels of polycytidylic acid-dependent adenosine triphosphatase, suggesting that the phenotype of the rho-111-bearing strain is the consequence of a single mutation. The rho-111 mutation was located on the S. typhimurium linkage map midway between the ilv and cya loci by phage P22 cotransduction studies. F' plasmid maintenance was not impaired in the mutant strain, and the mutation was recessive to the wild-type allele. The rho-111 mutation did not alter in vivo expression of either the tryptophan or histidine operons.

In vivo and in vitro detection of the leader RNA of the histidine operon of Escherichia coli K-12

The DNA of the attenuator region of the histidine operon of Escherichia coli has been transcribed in a purified in vitro system and found to synthesize two major RNA transcripts. The first one, 180 nucleotides long, has been identified as the histidine-specific leader RNA. It contains the coding sequence for the leader peptide [Di Nocera, P. P., Blasi, F., Di Lauro, R., Frunzio, R. & Bruni, C. B. (1978) Proc. Natl. Acad. Sci. USA 75, 4276-4280] and is terminated at the attenuator site. Termination of transcription at this site is extremely efficient in the in vitro system. The leader RNA also has been detected in vivo in a minicell producer strain transformed with plasmids harboring the regulatory region of the histidine operon of E. coli. A second RNA molecule is synthesized in the in vitro system. It has a divergent direction of transcription with respect to the histidine leader RNA, but its role, if any, in the regulation of the histidine operon remains to be ascertained. The existence of the histidine leader RNA lends support to the regulatory mechanism which postulates that regulation of the histidine operon is dependent on the alternative secondary structures that the leader RNA may assume, depending on whether or not the histidine-rich leader peptide is translated.

Possible regulation of the Salmonella typhimurium histidine operon by adenosine triphosphate phosphoribosyltransferase: large metabolic effects

An effort to find growth conditions leading to conditional regulation of the histidine operon of Salmonella typhimurium by the allosteric first enzyme of the pathway, adenosine triphosphate phosphoribosyltransferase (EC 2.4.2.17), is reported. A strain deleting the enzyme, TR3343, behaved simply and predictably under all growth conditions, whereas histidine auxotrophs containing active enzyme behaved in complicated ways dependent upon the location of the histidine pathway lesion. hisE strains derepressed the operon only one-half as much as TR3343 when grown on limiting histidine and a poor carbon source, but they also grew more slowly, probably as a result of high N1-(5-phospho-beta-D-ribosyl)-adenosine triphosphate levels in the cell. hisC strains exhibited oscillatory growth behavior and oscillatory histidine operon expression when grown on intermediate concentrations of the histidine precursor histidinol. This behavior probably was caused by synergistic in-phase variations in the histidine, purine nucleotide, and ppGpp pools of the cell. All of the growth and histidine operon expression effects associated with the presence of adenosine triphosphate phosphoribosyltransferase could be assigned to metabolic perturbation of the cell caused by unregulated enzymatic activity.

Structural and physiological studies of the Escherichia coli histidine operon inserted into plasmid vectors

A fragment of deoxyribonucleic acid 5,300 base paris long and containing the promoter-proximal portion of the histidine operon of Escherichia coli K-12, has been cloned in plasmid pBR313 (plasmids pCB2 and pCB3). Restriction mapping, partial nucleotide sequencing, and studies on functional expression in vivo and on protein synthesis in minicells have shown that the fragment contains the regulatory region of the operon, the hisG, hisD genes, and part of the hisC gene. Another plasmid (pCB5) contained the hisG gene and part of the hisD gene. Expression of the hisG gene in the latter plasmid was under control of the tetracycline promoter of the pBR313 plasmid. The in vivo expression of the two groups of plasmids described above, as well as their effect on the expression of the histidine genes not carried by the plasmids but present on the host chromosome, has been studied. The presence of multiple copies of pCB2 or pCB3, but not of pCB5, prevented derepression of the chromosomal histidine operon. Possible interpretations of this phenomenon are discussed.