Review of difficult airway management in thoracic surgery

The management of difficult airway (DA) in thoracic surgery is more difficult due to the need for lung separation or isolation and frequent presence of associated upper and lower airway problems. We performed an article review analysing 818 papers published with clinical evidence indexed in Pubmed that allowed us to develop an algorithm. The best airway management in predicted DA is tracheal intubation and independent bronchial blockers guided by fibroscopy maintaining spontaneous ventilation. For unpredicted DA, the use of videolaryngoscopes is recommended initially, and adequate neuromuscular relaxation (rocuronium/sugammadex), among other maneuvers. In both cases, double lumen tubes should be reserved for when lung separation is absolutely indicated. Finally, extubation should be a time of maximum care and be performed according to the safety measures of the Difficult Arway Society.

Results of treatment with azacitidine in patients aged ≥ 75 years included in the Spanish Registry of Myelodysplastic Syndromes

The tolerability of azacitidine (AZA) allows its administration in elderly patients. The objective of this study was to analyze the clinical and biological characteristics, transfusion independence (TI), overall survival (OS) and toxicity in a series of 107 patients ≥ 75 years of age from the Spanish Registry of Myelodysplastic Syndromes (MDS) treated with AZA. The median age (range) was 78 (75-90) years. According to the World Health Organization (WHO) classification, 86/102 (84%) had MDS, 10/102 (10%) had mixed myeloproferative/myelodysplastic disorder and 6/102 (6%) had acute myeloblastic leukemia. Regarding MDS by the International Prognostic Scoring System on initiation of AZA, 38/84 (45%) were low-intermediate-1 risk and 46/84 (55%) were intermediate-2-high risk. Ninety-five patients (89%) were red blood cell or platelet transfusion dependent. The AZA schedule was 5-0-0 in 39/106 (37%) patients, 5-2-2 in 36/106 (34%) patients and 7 consecutive days in 31/106 (29%) patients. The median number of cycles administered was 8 (range, 1-30). Thirty-eight out of 94 (40%) patients achieved TI. Median OS (95% confidence interval [CI]) was significantly better in patients achieving TI (n = 38) compared to patients who did not (n = 56) (22 [20.1-23.9] months vs. 11.1 [4.8-17.5] months, p = 0.001). No significant differences were observed in TI rate and OS among the three different schedules. With a median follow-up of 14 (min-max, 1-50) months, the median OS (95% CI) of the 107 patients was 18 (12-23) months and the probability of OS (95% CI) at 2 years was 34% (22-46%). Cycles were delayed in 31/106 (29%) patients and 47/101 patients (47%) were hospitalized for infection. These results show that treatment with AZA was feasible and effective in this elderly population, with 40% achieving TI, having a better OS than patients not achieving it. The schedule of AZA administration did not affect efficacy and toxicity.

[Orbital rhabdomyosarcoma: difficulties with European treatment protocol]

PURPOSE, MATERIAL AND METHODS: To present the experience in management of orbital rhabdomiosarcoma over 21 years in our centre. Review of the 12 cases of paediatric rhabdomiosarcoma and results of treatment in terms of mortality and morbidity comparing our results with other studies.

RESULTS/CONCLUSION

Management of orbital rhabdomyosarcoma following the European Protocol leads to poor results compared with the American protocol. Early radiotherapy and complete tumoral excision could play a role in management of this tumour

Modulation of Lrp action in Escherichia coli by leucine: effects on non-specific binding of Lrp to DNA

Lrp is a global regulator of metabolism in Escherichia coli that helps cells respond to changes in environmental conditions. The action of Lrp as a transcriptional activator or repressor is sometimes affected by whether the medium contains exogenous leucine. The abundance of Lrp in cells is relatively high (about 15 microM in monomer), and given the relatively high Lrp binding affinity in vitro for specific binding sites (nanomolar apparent dissociation constants), the expectation is that all binding sites will be saturated with Lrp in vivo. Here we consider the fraction of the total Lrp in cells that is free and the fraction that is bound to DNA. Using minicell-producing strains, we measured the distribution of Lrp between cytoplasm and nucleoid in cells grown under different nutritional conditions and in cells in different phases of growth. In E. coli cells grown in minimal medium to mid-log phase, the ratio of free to DNA-bound Lrp was about 0.67. This ratio decreased about threefold when the cells were grown in minimal medium supplemented with leucine. Our results also confirmed the previous finding that growth rate regulates lrp expression by as much as three to fourfold. Growth rate-regulated lrp expression, along with changes in the extent of non-specific binding, influences the level of free Lrp in vivo over a 16-fold range. We propose that the net effect of these processes is to regulate the relative concentrations of free Lrp hexadecamer and leucine-bound octamer, leading to promoter selection in response to environmental conditions.

Leucine-regulated self-association of leucine-responsive regulatory protein (Lrp) from Escherichia coli

Lrp is a global regulatory protein in Escherichia coli that activates expression of more than a dozen operons and represses expression of another dozen. For some operons, exogenous leucine reduces the extent of Lrp action, for others it potentiates the effect of Lrp, and for yet other operons it has no effect. In an effort to understand how leucine affects Lrp-mediated expression, we examined Lrp self-association and the effect of leucine on self-association using light scattering, chemical cross-linking, and analytical ultracentrifugation. The following results were obtained. (i) Lrp self-associates to a hexadecamer and octamer with the predominant species being hexadecamer at microM concentrations. (ii) Lrp undergoes a leucine-induced dissociation of hexadecamer to octamer. (iii) A mutant Lrp lacking 11 amino acid residues at the C terminus does not form higher-order oligomers, suggesting that the C terminus is involved in subunit association. (iv) At nM concentrations, Lrp dissociates to a dimer. It is proposed that leucine regulates the equilibrium between Lrp oligomers and thus Lrp occupancy of sites within different operons, leading to diverse regulatory patterns.

Global versus local regulatory roles for Lrp-related proteins: Haemophilus influenzae as a case study

Lrp (leucine-responsive regulatory protein) plays a global regulatory role in Escherichia coli, affecting expression of dozens of operons. Numerous lrp-related genes have been identified in different bacteria and archaea, including asnC, an E. coli gene that was the first reported member of this family. Pairwise comparisons of amino acid sequences of the corresponding proteins shows an average sequence identity of only 29% for the vast majority of comparisons. By contrast, Lrp-related proteins from enteric bacteria show more than 97% amino acid identity. Is the global regulatory role associated with E. coli Lrp limited to enteric bacteria? To probe this question we investigated LrfB, an Lrp-related protein from Haemophilus influenzae that shares 75% sequence identity with E. coli Lrp (highest sequence identity among 42 sequences compared). A strain of H. influenzae having an lrfB null allele grew at the wild-type growth rate but with a filamentous morphology. A comparison of two-dimensional (2D) electrophoretic patterns of proteins from parent and mutant strains showed only two differences (comparable studies with lrp(+) and lrp E. coli strains by others showed 20 differences). The abundance of LrfB in H. influenzae, estimated by Western blotting experiments, was about 130 dimers per cell (compared to 3,000 dimers per E. coli cell). LrfB expressed in E. coli replaced Lrp as a repressor of the lrp gene but acted only to a limited extent as an activator of the ilvIH operon. Thus, although LrfB resembles Lrp sufficiently to perform some of its functions, its low abundance is consonant with a more local role in regulating but a few genes, a view consistent with the results of the 2D electrophoretic analysis. We speculate that an Lrp having a global regulatory role evolved to help enteric bacteria adapt to their ecological niches and that it is unlikely that Lrp-related proteins in other organisms have a broad regulatory function.

[Pyogenic and non-pyogenic vertebral osteomyelitis: descriptive and comparative study of a series of 40 cases]

BACKGROUND

To describe the features of vertebral osteomyelitis (VO) in our area, and to compare pyogenic VO (PVO) and non-pyogenic VO (NPVO).

METHODS

Retrospective study of patients with VO diagnosed in our hospital between january 1992 and december 1998.

RESULTS

We identify 40 patients with VO: 17 (42.5%) with tuberculous VO, 12 (30%) with PVO, 10 (25%) with brucellar VO and 1 (2.5%) with a VO caused by Candida albicans. The mean age was 52.9 years, and 75% of patients were male. Only a 20% of cases had a known immunosuppression. Fever/febricule was present in 55% of patients and vertebral pain in 95%. The more frequent locations were lumbar (67.5%) and dorsal (27.5%). One or more paravertebral or epidural abscesses were present in 67.5% of cases and spinal cord compression was present in 27.5%. An elevated erythrocyte sedimentation rate (ESR) was present in 40% and leukocytosis in 27.5%. Sequelae after complete treatment occurred in 40% of patients, with residual vertebral pain in 37.5%. There was a shorter clinical course and a higher frequency of fever/febricule and leukocytosis in PVO than in NPVO.

CONCLUSIONS

In our area the more frequent etiology of VO is tuberculosis. VO occurs predominantly in males older than 50 years, without known immunosuppression, and almost exclusively with lumbar or dorsal locations. The absence of fever/febricule, leukocytosis or elevated ESR do not exclude the diagnosis of VO. Sequelae after complete treatment are relatively frequent, fundamentally residual vertebral pain. There are some differences in the features between PVO and NPVO, which may aid in the differential diagnosis of both entities.

Escherichia coli Lrp (leucine-responsive regulatory protein) does not directly regulate expression of the leu operon promoter

Studies by R. Lin et al. (J. Bacteriol. 174:1948-1955, 1992) suggested that the Escherichia coli leu operon might be a member of the Lrp regulon. Their results were obtained with a leucine auxotroph; in leucine prototrophs grown in a medium lacking leucine, there was little difference in leu operon expression between lrp(+) and lrp strains. Furthermore, when leuP-lacZ transcriptional fusions that lacked the leu attenuator were used, expression from the leu promoter varied less than twofold between lrp(+) and lrp strains, irrespective of whether or not excess leucine was added to the medium. The simplest explanation of the observations of Lin et al. is that the known elevated leucine transport capacity of lrp strains (S. A. Haney et al., J. Bacteriol. 174:108-115, 1992) leads to very high intracellular levels of leucine for strains grown with leucine, resulting in the superattenuation of leu operon expression.

[Access to bone marrow transplantation in acute myeloblastic leukemia. Study of 52 patients treated in a single center]

BACKGROUND

A single-center experience review about accessibility to bone marrow transplantation (BMT) as postremission therapy for acute myeloid leukemia (AML) is analyzed.

PATIENTS AND METHODS

From January 1988 to December 1994, 86 patients were diagnosed from de novo AML in our institution. A BMT was the treatment of choice for all patients younger than 55 years. An allogenic BMT (Allo-BMT) was offered for all patients younger than 35 years with a compatible sibling donor or those older patients, 35-55 years, with bad prognosis features. An autologus BMT (ABMT) was offered to those patients older than 35 years or those younger than 35 without an histocompatible donor.

RESULTS

52 out of 86 diagnosed patients were younger than 50 years (60%). 29 of them were candidates to Allo-BMT (24 patients younger than 35 years and 5 patients older than 35 with refractory disease) and the rest 23 to ABMT. 22 out of the 24 candidates to Allo-BMT entered complete remission (CR) and 12 of them had an HLA-identical donor. The Allo-BMT was performed in CR1 in 7 patients in CR2 in three patients and with refractory disease in two cases. An ABMT was finally planned in 30 patients, 18 patients older than 35 who entered CR and the rest 12 patients younger than 35 years in CR without a sibling donor. Only 11 out of this 30 patients underwent an ABMT in first CR. Reasons for this low number were: early relapse (B), toxicity (6), refuse (2), lost of follow-up (2) and suicide (1). Five out of this early relapse patients underwent an ABMT in CR2. Disease-free survival (DFS) at three years was 23 +/- 10% for the 52 patients included in the study. DFS obtained with Allo-BMT and AMBT were 39 +/- 16% and 63 +/- 22% respectively.

CONCLUSIONS

In spite of the new postremission treatment modalities available for AML the rate of longer survivals are still low. When data from BMT is analyzed we must be awared because only a small fraction of patients assigned to BMT will finally access to this treatment.

Effects of nutrition and growth rate on Lrp levels in Escherichia coli

Lrp (leucine-responsive regulatory protein) activates some Escherichia coli operons that function in anabolism and represses others involved in catabolism (for a review, see J. M. Calvo and R. G. Matthews, Microbiol. Rev. 58:466-490, 1994). This overall pattern suggests that Lrp may help cells adapt to changes in the nutritional environment. Here, we tested the idea that the nutritional richness of the medium determines the amount of Lrp in cells. Lrp was measured directly by Western blotting (immunoblotting) in cells grown in a chemically defined rich medium or in a minimal medium. In addition, transcription from the lrp promoter was assessed with a lacZ reporter gene. The results with these two different measurements were nearly the same, indicating that under the conditions employed, beta-galactosidase measurements can accurately reflect Lrp levels. For cells in a minimal medium, Lrp levels were consistently lowest during the logarithmic phase of growth, but overall, there was not much variation in levels as a function of growth phase (1.3-fold difference between highest and lowest values). However, for cells in a rich medium, Lrp levels dropped 3- to 4-fold during the lag phase, remained constant during the log phase, and then rose to starting levels upon entry into the stationary phase. When cells in the log phase were compared, Lrp levels were 3- to 4-fold higher in cells growing in a minimal medium than those in a rich medium. The levels of lrp expression were the same or slightly higher in strains containing mutations in rpoS, cya, or crp compared with wild-type strains, suggesting that neither RpoS nor the cyclic AMP (cAMP) receptor protein-cAMP complex is required for expression. On the other hand, lrp expression was severely restricted in cells that could not make ppGpp because of mutations in relA and spoT. The reduced expression of lrp during logarithmic growth in a rich medium may be due to low ppGpp levels under these conditions. The repressive effects of rich medium and the stimulatory effects of ppGpp were also observed with a construct having only a minimal lrp promoter (-57 to +21). The results of other experiments suggest that Lrp levels vary inversely with the growth rate of cells instead of being determined by some component of the medium.

The leucine-responsive regulatory protein (Lrp) from Escherichia coli. Stoichiometry and minimal requirements for binding to DNA

Lrp (Leucine-responsive regulatory protein) regulates the expression of a number of operons in Escherichia coli. A recent study of DNA sequences recognized by Lrp established the consensus as a 15-bp sequence, YAGHAWATTWTDCTR (Y = C/T, H = "not G," W = A/T, D ="not C," R = A/G) (Cui, Y., Wang, Q., Stormo, G. D., and Calvo, J. M. (1995) J. Bacteriol. 177, 4872-4880). Here we report the stoichiometry of Lrp binding (an Lrp dimer binds to a single binding site) and studies that define the minimal length of DNA required for binding. A double-stranded 15 mer having a sequence that closely matches the consensus does not show measurable binding to Lrp. One or two base pairs of DNA flanking each end are not sufficient for binding, but constructs having 3-5 additional base pairs (21 mer) show relatively strong binding. Single-stranded flanking DNA also contributes to strong binding. The extent of the contribution to binding is dependent upon whether the single strand is on the left or right of the double-stranded region and whether the polarity of the single-stranded DNA is 5' to 3' or 3' to 5'.

Prolonged enhancement of REM sleep produced by carbachol microinjection into the amygdala

The effect on sleep organization of carbachol microinjected into different amygdaloid nuclei was analysed in 12 cats. Single carbachol doses of 8 micrograms in 0.50 microliter saline were delivered unilaterally or bilaterally into the central, basal, lateral or basolateral amygdaloid nucleus. Carbachol administration into the central nucleus induced a prolonged (5 days) enhancement of both REM sleep and its preceeding slow wave sleep episodes with PGO waves (sommeil phasique a ondes lentes, SPHOL), which was more pronounced following bilateral than unilateral carbachol administration. However, neither SPHOL nor REM sleep changes were produced by administration of carbachol into the other amygdaloid nuclei. We conclude that cholinergic activation of the central amygdaloid nucleus produces a long-term facilitation of REM sleep occurrence.

A consensus sequence for binding of Lrp to DNA

Lrp (leucine-responsive regulatory protein) is a major regulatory protein involved in the expression of numerous operons in Escherichia coli. For ilvIH, one of the operons positively regulated by Lrp, Lrp binds to multiple sites upstream of the transcriptional start site and activates transcription. An alignment of 12 Lrp binding sites within ilvIH DNA from two different organisms revealed a tentative consensus sequence AGAAT TTTATTCT (Q. Wang, M. Sacco, E. Ricca, C.T. Lago, M. DeFelice, and J.M. Calvo, Mol. Microbiol. 7:883-891, 1993). To further characterize the binding specificity of Lrp, we used a variation of the Selex procedure of C. Tuerk and L. Gold (Science 249:505-510, 1990) to identify sequences that bound Lrp out of a pool of 10(12) different DNA molecules. We identified 63 related DNA sequences that bound Lrp and estimated their relative binding affinities for Lrp. A consensus sequence derived from analysis of these sequences, YAGHAWATTWT DCTR, where Y = C or T, H = not G, W = A or T, D = not C, and R = A or G, contains clear dyad symmetry and is very similar to the one defined earlier. To test the idea that Lrp in the presence of leucine might bind to a different subset of DNA sequences, we carried out a second selection experiment with leucine present during the binding reactions. DNA sequences selected in the presence or absence of leucine were similar, and leucine did not stimulate binding to any of the sequences that were selected in the presence of leucine. Therefore, it is unlikely that leucine changes the specificity of Lrp binding.

The amino acid sequence of Lrp is highly conserved in four enteric microorganisms

Lrp (leucine-responsive regulatory protein) is a global regulator of metabolism in Escherichia coli (J. M. Calvo and R. G. Matthews, Microbiol. Rev. 58:466-490, 1994). The lrp genes from three other enteric microorganisms, Enterobacter aerogenes, Klebsiella aerogenes, and Salmonella typhimurium, were cloned and sequenced. An analysis of these sequences and of the previously determined sequence from E. coli indicated that the vast majority of changes were synonymous rather than nonsynonymous changes. Nucleotide changes occurred at 89 of 492 positions but resulted in amino acid changes at only 2 of 164 positions. This analysis suggests that the Lrp amino acid sequence is highly adapted for function and that almost all amino acid changes lead to a protein that functions less well than the wild-type protein.

Sequence determinants of DNA bending in the ilvlH promoter and regulatory region of Escherichia coli

Previous studies have shown that the promoter/regulatory region of the ilvlH operon displays intrinsic curvature, with the bend center located at position -120 relative to the transcription start site. In this report, a 57 bp sequence spanning the bend center was mutagenized in vitro in order to study the relationship between nucleotide sequence and curvature measured by electrophoresis. The strategy used for analyzing the results consisted of determining the strengths of the relationships between electrophoretic anomaly and predicted curvature calculated by computer programs that differ in wedge angle composition. The results revealed that programs which assume that bending occurs only at AA/TT display good predictive value, with correlation coefficients between electrophoretic anomaly and predicted curvature as high as 0.93. In contrast, a program which assumes that bending occurs at all 16 dinucleotide steps exhibited lower predictive value, while there were no significant relationships between the experimental data and curvature calculated by a program that was based on all non-AA/TT wedge values. These results show that the complete wedge model which incorporates values for all dinucleotide steps does not adequately describe the electrophoretic data in this report.

Transitory and short-duration changes of sleep organization provoked by amygdaloid kindling in the cat: a daily 23-hour sleep recording study

The effect of amygdaloid kindling on sleep organization was tested in chronically implanted cats on a 12:12 light-dark cycle. Electrical kindling stimuli were delivered to the amygdala every 2 h during the light period. Total sleep time and percentage, mean duration, and mean number, as well as the hourly accumulation of waking (W) and sleep (slow wave sleep I and II, and paradoxical sleep) episodes were assessed from daily 23-h sleep recordings, consisting of baseline control recordings, control recordings where cats were briefly alerted at 2-h intervals to mimic the kindling trials manipulation, and recordings on each kindling day. The kindling process was completed within six days achieving three to five consecutive fully kindled seizures. Analysis of total recording time showed that the kindling process enhanced W stage and diminished total sleep time only on the second kindling day. Analysis of light and dark periods demonstrated compensatory W and sleep changes during the dark periods. Hourly sleep stage time accumulation was slowed during kindling trials, but compensated while stimuli were suspended. All of these changes returned to baseline values at the end of kindling. No significant differences between changes induced by kindling and those produced by alerting trials were found. We conclude that sleep alterations can not be exclusively attributed to kindling development, and that sleep is able to become adapted to the focal and generalized seizures effect.

The leucine-responsive regulatory protein, a global regulator of metabolism in Escherichia coli

The leucine-responsive regulatory protein (Lrp) regulates the expression of more than 40 genes and proteins in Escherichia coli. Among the operons that are positively regulated by Lrp are operons involved in amino acid biosynthesis (ilvIH, serA)), in the biosynthesis of pili (pap, fan, fim), and in the assimilation of ammonia (glnA, gltBD). Negatively regulated operons include operons involved in amino acid catabolism (sdaA, tdh) and peptide transport (opp) and the operon coding for Lrp itself (lrp). Detailed studies of a few members of the regulon have shown that Lrp can act directly to activate or repress transcription of target operons. A substantial fraction of operons regulated by Lrp are also regulated by leucine, and the effect of leucine on expression of these operons requires a functional Lrp protein. The patterns of regulation are surprising and interesting: in some cases activation or repression mediated by Lrp is antagonized by leucine, in other cases Lrp-mediated activation or repression is potentiated by leucine, and in still other cases leucine has no effect on Lrp-mediated regulation. Current research is just beginning to elucidate the detailed mechanisms by which Lrp can mediate such a broad spectrum of regulatory effects. Our view of the role of Lrp in metabolism may change as more members of the regulon are identified and their regulation characterized, but at this point Lrp seems to be important in regulating nitrogen metabolism and one-carbon metabolism, permitting adaptations to feast and to famine.

Regulation of the Escherichia coli lrp gene

Lrp (leucine-responsive regulatory protein) is a major Escherichia coli regulatory protein which regulates expression of a number of operons, some negatively and some positively. This work relates to a characterization of lrp, the gene encoding Lrp. Nucleotide sequencing established that the coding regions of lrp and trxB (encoding thioredoxin reductase) are separated by 543 bp and that the two genes are transcribed in opposite directions. In addition, we used primer extension, deletion analyses, and lrp-lacZ transcriptional fusions to delineate the promoter and regulatory region of the lrp operon. The lrp promoter is located 267 nucleotides upstream of the translational start codon of the lrp gene. In comparison with a wild-type strain, expression of the lrp operon was increased about 3-fold in a strain lacking Lrp and decreased about 10-fold in a strain overproducing Lrp. As observed from DNA mobility shift and DNase I footprinting analyses, Lrp binds to one or more sites within the region -80 to -32 relative to the start point of lrp transcription. A mutational analysis indicated that this same region is at least partly required for repression of lrp expression in vivo. These results demonstrate that autogenous regulation of lrp involves Lrp acting directly to cause repression of lrp transcription.

Transcriptional termination. Charging it cancels the order

In a newly discovered mechanism for regulating transcription termination, a cognate uncharged tRNA acts directly to promote transcription readthrough.

Regions of the Bacillus subtilis ilv-leu operon involved in regulation by leucine

The ilv-leu operon of Bacillus subtilis is regulated in part by transcription attenuation. The cis-acting elements required for regulation by leucine lie within a 683-bp fragment of DNA from the region upstream of ilvB, the first gene of the operon. This fragment contains the ilv-leu promoter and 482 bp of the ilv-leu leader region. Spontaneous mutations that lead to increased expression of the operon were shown to lie in an imperfect inverted repeat encoding the terminator stem within the leader region. Mutations within the inverted repeat of the terminator destroyed most of the leucine-mediated repression. The remaining leucine-mediated repression probably resulted from a decrease in transcription initiation. A systematic analysis of other deletions within the ilv-leu leader region identified a 40-bp region required for the derepression that occurred during leucine limitation. This region lies within a potential RNA stem-and-loop structure that is probably required for leucine-dependent control. Deletion analysis also suggested that alternate secondary structures proximal to the terminator are involved in allowing transcription to proceed beyond the terminator. Additional experiments suggested that attenuation of the ilv-leu operon is not dependent on coupling translation to transcription of the leader region. Our data support a model proposed by Grundy and Henkin (F. J. Grundy and T. M. Henkin, Cell 74:475-482, 1993) in which uncharged tRNA acts as a positive regulatory factor to increase gene expression during amino acid limitation.

Lrp, a major regulatory protein in Escherichia coli, bends DNA and can organize the assembly of a higher-order nucleoprotein structure

Lrp (Leucine-responsive regulatory protein) is a global regulatory protein that controls the expression of many operons in Escherichia coli. One of those operons, ilvIH, contains six Lrp binding sites located within a several hundred base pair region upstream of the promoter region. Analysis of the binding of Lrp to a set of circularly permuted DNA fragments from this region indicates that Lrp induces DNA bending. The results of DNase I footprinting experiments suggest that Lrp binding to this region facilitates the formation of a higher-order nucleoprotein structure. To define more precisely the degree of bending associated with Lrp binding, one or two binding sites were separately cloned into a pBend vector and analyzed. Lrp induced a bend of approximately 52 degrees upon binding to a single binding site, and the angle of bending is increased to at least 135 degrees when Lrp binds to two adjacent sites. Lrp-induced DNA bending, and a natural sequence-directed bend that exists within ilvIH DNA, may be architectural elements that facilitate the assembly of a nucleoprotein complex.

Organization of Lrp-binding sites upstream of ilvIH in Salmonella typhimurium

Lrp, a major regulatory protein in Escherichia coli, controls the expression of numerous operons, including ilvIH. Lrp binds to six sites upstream of ilvIH, and Lrp binding is required for ilvIH expression. We show here that an Lrp-like protein is also present in Salmonella typhimurium. This protein can bind both E. coli and S. typhimurium ilvIH DNA, as can E. coli Lrp. Methidiumpropyl-EDTA footprinting studies were performed with purified E. coli Lrp and S. typhimurium ilvIH DNA. Six binding sites were defined, three of them being similar to corresponding sites in E. coli, and three being organized differently. A consensus derived from six S. typhimurium sites is compatible with that derived from a similar analysis of E. coli sequences.

Mutations affecting the ability of Escherichia coli Lrp to bind DNA, activate transcription, or respond to leucine

Lrp is a regulatory protein in Escherichia coli that increases expression of some operons and decreases expression of others. Mutations in Lrp were isolated on the basis of their effects on ilvIH, one of the operons regulated positively by Lrp. The ilvIH operon encodes an enzyme involved in the biosynthesis of leucine, valine, and isoleucine, and expression of this operon is repressed when cells are grown in the presence of leucine. Three groups of mutants were isolated. Mutant strains that were resistant to the repressive effects of leucine were termed leucine response mutants. These mutants had changes in the Lrp amino acid sequence between amino acid residues 108 and 149. Mutant strains having low expression of ilvIH in vivo were identified as colonies having reduced expression of a reporter gene. For some of these mutants, called DNA-binding mutants, binding to ilvIH DNA in vitro was markedly reduced. The mutations in these strains caused changes in Lrp between amino acids 16 and 70. Six of ten of these mutations were within a region having a putative helix-turn-helix motif. A third group of mutants had low ilvIH expression in vivo but apparently normal DNA binding in vitro. These mutants were called activation mutants since they affected the ability of Lrp to activate expression. Lrp from these strains had changes in amino acids between residues 76 and 125. This study suggests that Lrp has separate domains responsible for binding DNA, activating transcription, and responding to leucine.

Lrp, a global regulatory protein of Escherichia coli, binds co-operatively to multiple sites and activates transcription of ilvIH

Lrp (Leucine-responsive regulatory protein) has recently been recognized as a major regulatory protein that controls the expression of many operons in Escherichia coli. Footprinting and gel retardation experiments with DNA from ilvIH, one of the operons controlled positively by Lrp, indicate that Lrp binds to six sites over a 200 base-pair region upstream from the promoter. Binding of Lrp to some of these sites is highly co-operative. We suggest a consensus sequence for Lrp binding based upon a comparison of six binding sites. An analysis of mutants indicates that five out of six binding sites are important for transcription activation and that two or three adjacent Lrp binding sites act synergistically in vivo. The observed synergistic effects in vivo may result from co-operative binding of Lrp to adjacent sites. We propose a model in which multiple binding sites contribute to the formation of a nucleoprotein complex, but only a particular proximal site positions Lrp properly so that it interacts with RNA polymerase.

In vitro transcription from the Escherichia coli ilvIH promoter

Lrp (leucine-responsive regulatory protein) activates the expression of the Escherichia coli ilvIH operon in vivo and mediates the repression of the operon by exogenous leucine. In previous studies, operon expression in vivo was measured with transcriptional fusions of lacZ to the ilvIH promoter. Here, ilvIH mRNA was measured directly by primer extension. The steady-state level of ilvIH mRNA was 11-fold higher in a wild-type parent strain than in a derivative lacking Lrp. A two-step procedure was developed for measuring ilvIH mRNA synthesized in vitro. RNA was synthesized with plasmid templates and purified RNA polymerase, and then ilvIH mRNA was measured by primer extension. In vitro, mRNA synthesis was initiated at two sites, one corresponding to the in vivo site (promoter P1) and the other corresponding to a site about 60 bp further upstream (promoter P2). Purified Lrp stimulated transcription two- to fivefold from promoter P1, whereas it decreased transcription more than fivefold from promoter P2. Transcription from promoter P1 was stimulated by Lrp with templates containing the wild-type ilvIH promoter but not with templates containing mutations in an Lrp binding site. Furthermore, under at least some conditions, leucine reversed the stimulatory effect of Lrp. Taken together with the results of mutational analyses, these results establish that Lrp acts directly to stimulate transcription from the ilvIH promoter. Furthermore, they suggest that the ilvIH promoter is recognized by a sigma 70 RNA polymerase.

Cholinergic microstimulation of the peribrachial nucleus in the cat. II. Delayed and prolonged increases in REM sleep

The hypothesis that REM sleep is cholinergically mediated is supported by the identification of a cholinoceptive trigger zone in the FTG. Since this trigger zone is devoid of cholinergic neurons, the aim of the present study was to test the hypothesis that a cholinergic drive for REM sleep may come from the cholinergic cells of the PBL region. Chronically implanted freely moving cats with electrodes for sleep and PGO wave recordings were used. Guide tubes were implanted for carbachol microinjections (4 micrograms/250 nl) in the PBL and FTG. All microinjections were delivered in close vicinity of ChAT+ cholinergic cells in the PBL region. Results showed that a single unilateral carbachol microinjection into the PBL induced sustained (24 hr) state-independent ipsilateral PGO wave activity. This PGO wave activity was followed by a prolonged enhancement of REM sleep lasting for more than six days. We also observed that REM enhancement was followed by a delayed but marked enhancement of S sleep episodes with PGO waves (SP), which are normally brief transitions from S to REM sleep. Our findings strongly support the hypothesis that cholinergic drive for REM sleep comes from the lateral pontine tegmentum and we suggest that the PBL region plays a major role in both PGO wave generation and long-term regulation of REM sleep induction.

Cholinergic microstimulation of the peribrachial nucleus in the cat. I. Immediate and prolonged increases in ponto-geniculo-occipital waves

The cholinergic agonist carbachol was injected into the pontine Pb area where PGO bursting cells have been recorded. When microinjections were localized to the ventrolateral aspect of the caudal Pb nucleus near aggregates of ChAT immunolabeled cholinergic neurons, carbachol produced an immediate onset of state-independent PGO waves in the ipsilateral LGB. These state-independent PGO waves persisted for 3-4 days. After the first 24 hrs PGO wave activity increasingly became associated with REM sleep and with REM transitional SP sleep as both of these PGO-related states increased in amount to 3-4 times baseline levels. The increase in amount of PGO-related states peaked on days 2-4 following one carbachol injection and persisted for 10-12 days. These results suggest a two stage process: stage one, PGO enhancement, is the direct consequence of the membrane activation of cholinoceptive PGO burst neurons by carbachol; stage two, REM enhancement, is the consequence of metabolic activation of endogenous cholinergic neurons. This experimental preparation is a useful model for the study of the electrophysiology and functional significance of PGO wave and REM sleep generation.

Leucine-responsive regulatory protein controls the expression of both the pap and fan pili operons in Escherichia coli

The methylation blocking factor gene (mbf) in Escherichia coli is required for specific methylation inhibition of two DNA GATC sites upstream of the papBA pilin promoter and transcriptional activation of pap. Complementation and mutational analysis using pap-lac and ilvIH-lac operon fusions indicates that the mbf gene is identical to a recently described global regulatory gene lrp (leucine-responsive regulatory protein) that acts as a positive regulator of some genes and a negative regulator of others in E. coli. DNA sequence analysis of an mbf::mTn10 insertion showed that the mbfDNA sequence was identical to lrp. Thus Lrp inhibits DNA methylation at specific GATC sites. We also show that Lrp positively regulates transcription of the fan operon, which encodes K99 pili of diarrheagenic E. coli. Purified Lrp was found to bind to DNA fragments encompassing the pap and fan promoters, which is consistent with previous results indicating that Lrp controls gene expression by binding to regulatory DNA sites. Exogenous leucine significantly reduced fan transcription and K99 pili expression, similar to results obtained with the ilvIH operon. However, pap gene expression was unresponsive to leucine, which distinguishes pap from other lrp-regulated genes whose expression is modulated by leucine.

Transcriptional regulation of the ilv-leu operon of Bacillus subtilis

We used primer extension and mutational analysis to identify a promoter upstream of ilvB, the first gene in the ilv-leu operon of Bacillus subtilis. Between the promoter and ilvB, there is a 482-bp leader region which contains a sequence that resembles a factor-independent transcription terminator. In in vitro transcription experiments, 90% of transcripts initiated at the ilvB promoter ended at a site near this terminator. Primer extension analysis of RNA synthesized in vivo showed that the steady-state level of mRNA upstream of the terminator was twofold higher from cells limited for leucine than it was from cells grown with excess leucine. mRNA downstream of the terminator was 14-fold higher in cells limited for leucine than in cells grown with excess leucine. Measurement of mRNA degradation rates showed that the half-life of ilv-leu mRNA was the same when the cells were grown with or without leucine. These data demonstrate that the ilv-leu operon is regulated by transcription attenuation.

Lrp, a leucine-responsive protein, regulates branched-chain amino acid transport genes in Escherichia coli

We investigated the relationship between two regulatory genes, livR and lrp, that map near min 20 on the Escherichia coli chromosome. livR was identified earlier as a regulatory gene affecting high-affinity transport of branched-chain amino acids through the LIV-I and LS transport systems, encoded by the livJ and livKHMGF operons. lrp was characterized more recently as a regulatory gene of a regulon that includes operons involved in isoleucine-valine biosynthesis, oligopeptide transport, and serine and threonine catabolism. The expression of each of these livR- and lrp-regulated operons is altered in cells when leucine is added to their growth medium. The following results demonstrate that livR and lrp are the same gene. The lrp gene from a livR1-containing strain was cloned and shown to contain two single-base-pair substitutions in comparison with the wild-type strain. Mutations in livR affected the regulation of ilvIH, an operon known to be controlled by lrp, and mutations in lrp affected the regulation of the LIV-I and LS transport systems. Lrp from a wild-type strain bound specifically to several sites upstream of the ilvIH operon, whereas binding by Lrp from a livR1-containing strain was barely detectable. In a strain containing a Tn10 insertion in lrp, high-affinity leucine transport occurred at a high, constitutive level, as did expression from the livJ and livK promoters as measured by lacZ reporter gene expression. Taken together, these results suggest that Lrp acts directly or indirectly to repress livJ and livK expression and that leucine is required for this repression. This pattern of regulation is unusual for operons that are controlled by Lrp.

Long-term enhancement of REM sleep following cholinergic stimulation

A six day long increase in rapid eye movement (REM) sleep followed the unilateral microinjection of a single dose of the cholinergic agonist drug carbachol into the brain stem of cats. Effective drug injection sites were localized to the pontine peribrachial region containing cholinergic choline acetyltransferase (ChAT) labeled neurons. At the peak of the effect, which occurred 24-28 h post-injection, the relative amount of time devoted to REM sleep tripled, resulting in an absolute time increase from 3.12 to 11.28 h REM sleep per day. This pronounced and prolonged REM sleep increase was associated with marked enhancement of ponto-geniculo-occipital (PGO) waves and with PGO burst cell activity unilateral to the site of injection.

Amygdaloid kindling during wakefulness and paradoxical sleep in the cat. 2. Sleep organization changes produced by kindling development

The effect of daily electrical amygdaloid stimulation (kindling, K) during waking (W-K) and paradoxical sleep (PS-K) on sleep organization was tested in 2 groups of chronically implanted adult male cats. Animals were stimulated 3 h after the 8-h sleep recordings were begun. Percentage, total time, and mean duration and number of episodes of W, slow wave sleep I and II, and PS stages were determined. Also, the mean interval of occurrence and hourly accumulation of PS were assessed. Recordings were performed before, throughout, and immediately after kindling and 2 months after the last recorded kindled seizures. Analysis of total recording time demonstrated that in both W-K and PS-K animals the kindling process provoked only transitory changes which returned to baseline values during kindling and immediately after. Analysis of pre- and post-stimulation periods demonstrated compensatory changes in W and PS percentage during the late stages of kindling. We conclude that rather than sleep diminution, kindling provokes a circadian shift of W and PS stages.

Amygdaloid kindling during wakefulness and paradoxical sleep in the cat. 1. Inhibitory influence of paradoxical sleep on kindling development

The development of amygdaloid kindling during wakefulness (W) and paradoxical sleep (PS) was compared in chronically implanted adult male cats. The animals were divided into 2 groups. One group was kindled during W (W-K) and the second during a burst of pontogeniculo-occipital (PGO) potentials during PS (PS-K). The threshold of amygdaloid afterdischarge (AD) was determined during W in the W-K group and during PS in the PS-K group. For the development of kindling, amygdala stimulation was applied daily. Results demonstrate that kindling development was markedly retarded in the PS-K group. From the first kindling trials, mean AD duration in the PS-K group was significantly shorter than in the W-K group and this difference was sustained until generalized convulsive seizures (GCSs) were reached by the W-K animals. Also, mean AD frequency in the PS-K group was significantly lower than in the W-K group. AD propagation to the contralateral amygdala and sensorimotor cortex was significantly retarded in the PS-K animals. Time spent in behavioral stages I and II of kindling was significantly longer in the PS-K animals than in W-K animals and the number of daily electrical stimuli required to reach the first GCS was significantly higher in group PS-K than in group W-K. It is concluded that PS exhibits an inhibitory influence over amygdaloid kindling development and this influence is mainly exerted during the early stages of epileptogenesis.

Characterization of Lrp, and Escherichia coli regulatory protein that mediates a global response to leucine

Exogenous leucine affects the expression of a number of different operons in Escherichia coli. For at least some of these operons, the leucine-related effect is mediated by a protein called Lrp (Leucine-responsive regulatory protein). The purification of Lrp to near homogeneity is described. Lrp is a moderately abundant, basic protein composed of two subunits of molecular mass 18.8 kDa each. In addition, the corresponding protein was purified from a strain having a mutation within the gene that encodes Lrp (lrp). This mutation (lrp-1) causes high constitutive expression of ilvIH, one of the operons controlled by Lrp (Platko, J. V., Willins, D.A., and Calvo, J.M. (1990) J. Bacteriol. 172, 4563-4570). The Lrp-1 and Lrp proteins have similar physical properties, but they show some differences in the characteristics with which they bind DNA upstream of the ilvIH promoter. The nucleotide sequences of the lrp and lrp-1 genes differ by only a single nucleotide, a C to G change that would substitute a Glu for an Asp at amino acid 114. Lrp has some amino acid sequence similarity to AsnC, a protein that regulates asnA expression (Kolling, R., and Lother, H. (1985) J. Bacteriol. 164, 310-315).

The ilvIH operon of Escherichia coli is positively regulated

The ilvIH operon of Escherichia coli (located near min 2) encodes acetohydroxyacid synthase III, an isozyme involved in branched-chain amino acid biosynthesis. A strain with lacZ fused to the ilvIH promoter was constructed. Transposon Tn10 was introduced into this strain, and tetracycline-resistant derivatives were screened for those in which ilvIH promoter expression was markedly reduced. In one such derivative, strain CV1008, beta-galactosidase expression was reduced more than 30-fold. The transposon giving rise to this phenotype inserted near min 20 on the E. coli chromosome. Extract from a wild-type strain contains a protein, the IHB protein, that binds to two sites upstream of the ilvIH promoter (E. Ricca, D. A. Aker, and J. M. Calvo, J. Bacteriol. 171:1658-1664, 1989). Extract from strain CV1008 lacks IHB-binding activity. These results indicate that the IHB protein is a positive regulator of ilvIH operon expression. The gene that encodes the IHB protein, ihb, was cloned by complementing the transposon-induced mutation. Definitive evidence that the cloned DNA encodes the IHB protein was provided by determining the sequence of more than 17 amino acids at the N terminus of the IHB protein and comparing it with the nucleotide sequence. A mutation that prevents repression of the ilvIH operon by leucine in vivo and that alters the DNA-binding characteristics of the IHB protein in vitro was shown to be an allele of the ihb gene. The ihb gene is identical to oppI, a gene that regulates the oppABCDF operon (E. A. Austin, J. C. Andrews, and S. A. Short, Abstr. Mol. Genet. Bacteria Phages, p. 153, 1989). Thus, oppI/ihb encodes a protein that regulates both ilvIH, an operon that is repressed by leucine, and oppABCDF, an operon involved in peptide transport that is induced by leucine. We propose that the designation lrp be used in the future instead of oppI or ihb and that Lrp (leucine-responsive regulatory protein) be used in place of IHB.

Transcriptional proofreading in Escherichia coli

A novel transcriptional proofreading mechanism associated with the beta-subunit of wild-type RNA polymerase from Escherichia coli is suggested from the following data. The purified holoenzyme contains an NTPase activity which specifically converts noncognate NTPs to their corresponding NDP in a template-dependent manner during in vitro transcription of synthetic single- and double-stranded templates. In contrast, purified enzyme from an rpoB mutant which shows increased transcriptional error lacked template-dependent NTP hydrolytic activity. The NTP hydrolytic activity of wild-type enzyme was critically dependent on the integrity of the initiation complex, and required continued transcriptional elongation. Transcription and translation of the lacZ gene proceeded 17% faster in the mutant than in its wild-type parent. These results are discussed in terms of a proofreading model in which the rate of transcription is limited by proofreading events that involve recognition and hydrolysis of noncognate NTPs before they can be misincorporated into RNA.

Massed amygdaloid kindling in encéphale isolé cats: its facilitation by naloxone

The effect of repetitive administration of naloxone on the development of massed amygdaloid kindling in 'encéphale isolé' cats was studied. Electrical amygdaloid kindling was carried out with a 15 min inter-stimulus interval (ISI) in a control situation with intravenous (i.v.) naloxone administration (2, 4, and 8 mg/kg), 5 min prior to amygdaloid stimulation. It was found that it was possible to complete the amygdaloid kindling process in the encéphale isolé preparation reaching generalized electrographic tonic-clonic self-sustained seizures. The enhancement of the duration, frequency, and propagation of the after-discharge (AD) was accentuated by naloxone which also induced a progressive amplitude increment of the first potential evoked by the onset of the tetanus. The number of trials needed to achieve seizure generalization was reduced in dose-dependent manner by naloxone. The ability of naloxone to accelerate the development of amygdaloid kindling may be related to an inhibitory role of opioid peptides in this process.

A protein that binds to the regulatory region of the Escherichia coli ilvIH operon

The ilvIH operon of Escherichia coli encodes acetohydroxyacid synthase III, an isoenzyme involved in branched-chain amino acid biosynthesis. Transcription of the ilvIH operon is repressed by growing cells in the presence of leucine (C.H. Squires, M. DeFelice, S.R. Wessler, and J.M. Calvo, J. Bacteriol. 147:797-804, 1981). A protein in crude extracts of E. coli, termed the ilvIH-binding (IHB) protein, bound specifically in vitro to DNA upstream of the ilvIH operon. The binding protein, partially purified by Polymin precipitation, gel filtration, and phosphocellulose chromatography, has a native molecular weight of 43,000 and is composed of two subunits of identical size. As determined by protection against lambda exonuclease and DNase I, the protein binds within a region -190 to -260 relative to the start point of transcription. In addition, the IHB protein binds to a site between positions -100 and -40. The following evidence suggests that binding of this protein to the region upstream of ilvIH is related to the regulation of this operon by leucine. Binding of the IHB protein to the ilvIH regulatory region in vitro was reduced by leucine but not by isoleucine, valine, or threonine. In a mutant strain isolated by M.V. Ursini, P. Arcari, and M. DeFelice (Mol. Gen. Genet. 181:491-496, 1981), transcription was not repressed by leucine. A protein in extracts of this mutant strain bound to the ilvIH regulatory region, but the complex migrated through agarose gels with a mobility different from that of the complex formed by wild-type protein. Furthermore, a concentration of leucine that substantially reduced binding of the wild-type to DNA did not affect binding of the protein from the mutant strain. A simple model consistent with these findings is that transcription from the ilvIH promoter is stimulated by binding the IHB protein to one or more sites upstream of the promoter and that leucine interferes with this binding.

A large family of bacterial activator proteins

At least nine different bacterial proteins belong to the LysR family. The gene sequence for one of these proteins is presented here. Six others (Escherichia coli LysR, IlvY, CysB; Salmonella typhimurium MetR; Rhizobium NodD; and Enterobacter cloacae AmpR) are known to activate other genes. Based on sequence alignments, each member of this family is predicted to have a helix-turn-helix DNA binding motif near its amino terminus. The combined evidence indicates that all nine proteins are related by common ancestry, are similarly folded, and are not detectably related to other known bacterial regulatory proteins. The DNA database searching procedure and other methods used in this study should be useful in detecting other groups of related proteins.