Characterization of a glucose transport system in Vibrio parahaemolyticus

Cells of a glucose-PTS (phosphoenolpyruvate:carbohydrate phosphotransferase system)-negative mutant of Vibrio parahaemolyticus transport D-glucose in the presence of Na+. Maximum stimulation of D-glucose transport was observed at 40 mM NaCl, and Na+ could be replaced partially with Li+. Addition of D-glucose to the cell suspension under anaerobic conditions elicited Na+ uptake. Thus, we conclude that glucose is transported by a Na+/glucose symport mechanism. Calculated Vmax and Km values for the Na(+)-dependent D-glucose transport were 15 nmol/min/mg of protein and 0.57 mM, respectively, when NaCl was added at 40 mM. Na+ lowered the Km value without affecting the Vmax value. D-Glucose was the best substrate for this transport system, followed by galactose, alpha-D-fucose, and methyl-alpha-glucoside, judging from the inhibition pattern of the glucose transport. D-Glucose itself partly repressed the transport system when cells were grown in its presence.

F0F1-ATPase of Vibrio parahaemolyticus: purification using new detergents and characterization

Previous attempts to isolate a stable F0F1-ATPase complex (H(+)-translocating ATPase) from Vibrio parahaemolyticus have been unsuccessful. Using new non-ionic detergents (alkyl thiomaltosides), a stable F0F1 complex with a high specific activity (15-25 units/mg protein) was purified and characterized. The purified F0F1-ATPase consists of eight subunits (alpha, beta, gamma, delta, epsilon, a, b and c). The new detergents, in combination with sucrose (or glycerol), lipid, dithiothreitol and phenylmethylsulfonyl fluoride, effectively stabilized the F0F1 complex. The ATPase activity of the F0F1 complex was greatly increased by anions, such as SO4(2-) and SO3(2-). Sodium ion increased the activity by about 2-fold. Dicyclohexylcarbodiimide, Zn2+, 4-acetamido-4'-isothiocyanostilben-2,2'disulfonate and tetrachlorosalicylanilide inhibited F0F1-ATPase activity. Ethanol, which stimulated F1-ATPase activity, inhibited F0F1-ATPase activity. Methanol, Na3VO4 and bafilomycin A1 did not have any significant effect on F0F1-ATPase activity, although methanol, like ethanol, stimulated F1-ATPase activity.

Properties and sequence of the NhaA Na+/H+ antiporter of Vibrio parahaemolyticus

A gene encoding an Na+/H+ antiporter was cloned from chromosomal DNA of the slightly halophilic marine bacterium Vibrio parahaemolyticus. The host was an Escherichia coli mutant that lacked both of the two major Na+/H+ antiporters, NhaA and NhaB. Untransformed mutant cells were unable to grow in the presence of 0.6 M NaCl or 0.1 M LiCl, but Na+ and Li+ were non-toxic to cells transformed with a plasmid carrying the antiporter gene. Membrane vesicles prepared from the original E. coli mutant did not show any detectable Na+/H+ (and Li+/H+) antiport activity. However, we observed high Na+/H+ (and Li+/H+) antiport activity in membrane vesicles prepared from the transformed cells. The activity increased greatly when the pH of the assay medium was increased from 7.0 and 8.5. This property is very similar to that of the NhaA Na+/H+ antiporter of E. coli. Drastic decreases in Km values for Li+ and Na+ were observed with membrane vesicles prepared from the transformed cells compared with those observed with V. parahaemolyticus vesicles. The amino acid sequence deduced from the nucleotide sequence of the cloned gene showed high homology (59% identity and 87% similarity) with the NhaA Na+/H+ antiporter of E. coli. Thus, we conclude that the gene we cloned and sequenced is the nhaA of V. parahaemolyticus. We also found that several regions of the NhaA protein showed sequence similarity with transport proteins from some other organisms. Such regions seem to be important for Na+ recognition, transport or amiloride binding.

Differential expression of sgk mRNA, a member of the Ser/Thr protein kinase gene family, in rat brain after CNS injury

We cloned genes the expression of which were induced 3 days after cortical injury of rat brain by a differential display technique, and four novel and known sequences were isolated. Among these sequences, the sgk gene which was recently identified as a novel member of the serine/threonine protein kinase gene family, was selected for analysis of its expression patterns in rat brain by northern blotting and in situ hybridization, because hybridization signals were strong at the lesion sites. Expression of sgk mRNA was induced within 3 days after injury, and was maintained at a high level for at least 14 days. The cells which strongly expressed the sgk gene were in the deep layers of the cortex and in the corpus callosum. In situ hybridization analysis for sgk and myelin proteolipid protein mRNA using serial sections showed that the distribution of both signals was very similar at the damaged regions. Therefore, it is likely that the sgk transcript is expressed by oligodendrocytes after brain injury. Investigation of the developmental expression of the sgk gene showed that neurons in layers I and II of the cortex, lateroposterior and laterodorsal thalamic nucleus, and ventral posterolateral and posteromedial thalamic nucleus strongly expressed sgk mRNA at postnatal day 1 and day 7, but these neurons showed no expression in fetal or adult brain. These results suggest that the induction of sgk gene may be associated with a series of axonal regenerations after brain injury, and in addition, the sgk gene may also play important roles in the development of particular groups of neurons in the postnatal brain.

[Osteoporosis in congenital disorders]

Osteogenesis imperfecta (OI) is the most prevalent osteoporosis syndrome in childhood and is characterized by fractures and skeletal deformities. In almost all individuals, OI results from mutations in one of the two genes (COL1A1 and COL1A2) that encode the chains of type I collagen. OI can be divided into four major groups, type I, II, III, and IV, that differ in clinical presentation, mode of inheritance, radiographic picture, and, for the most part, the biochemical basis of the connective disorder. The molecular basis of OI is mainly discussed.

Modulation of AP-1 activity by nitric oxide (NO) in vitro: NO-mediated modulation of AP-1

To understand the role of nitric oxide (NO) in controlling the specific DNA-binding activities of transcriptional factors, we investigated the in vitro effect of the NO-donor sodium nitroprusside (SNP) on the AP-1 activity of cultured mouse cerebellar granule cells. A gel-mobility assay showed that SNP inhibited AP-1 activity in the presence, but not the absence of dithiothreitol (DTT). This DTT-dependent inhibition of AP-1 activity by SNP corresponded with the activation of the chemical reactivity of SNP with DTT, which can be monitored by the production of nitrite (NO2-). In contrast, diamide, a typical sulfhydryl oxidizing agent, inhibited AP-1 activity in the absence of DTT and its inhibitory effect was reversed competitively by DTT. Studies using structurally or functionally related analogues of SNP demonstrated that S-nitrosylation of the AP-1 moiety mediated by some NO-carriers but not by free NO, which can be produced by the chemical reaction of SNP with DTT, was responsible for the inhibition of AP-1 activity, suggesting NO-mediated regulation of the AP-1 transcriptional factor.

A new protocol and criteria for quantitative determination of sensitization potencies of chemicals by guinea pig maximization test

This paper presents precise sensitization test data of 15 chemicals with a wide spectrum of sensitization potencies, and proposes a new protocol and criteria for quantitative evaluation of sensitization potencies of chemicals. The tests were performed according to the design of Magnusson and Kligman, changing the application concentrations for induction as well as for challenge phases. 3-dimensional relationships between mean response (or sensitization rate), induction and challenge concentrations were found in all chemicals tested. The following 2 values are proposed as a quantitative measure of sensitization potency: (a) the minimum induction concentration that induces a positive response; (b) the challenge concentration that induces a mean response approximately equal to 1.0 among the animals applied with the highest concentration for induction. Both values coincided with each other within the range of 1 order of magnitude in every compound except 2. The values varied by 5 orders or more of magnitude among the compounds, showing a wide variation of sensitization potencies among chemicals. A good correlation was found for every chemical between the value of sensitization potency thus obtained and the residual levels in causative products in human cases of allergic contact dermatitis. A new experimental protocol for obtaining values (a) and (b) is proposed.

The NhaB Na+/H+ antiporter is essential for intracellular pH regulation under alkaline conditions in Escherichia coli

We isolated a mutant of Escherichia coli which was defective in an Na+/H+ antiporter and grew poorly under alkaline conditions [Ishikawa, T., Hama, H., Tsuda, T., and Tsuchiya, T. (1987) J. Biol. Chem. 262, 7443-7446]. Later, it was concluded that the defective Na+/H+ antiporter in the mutant was the NhaB system, and the nhaB gene was mapped to 25.6 min on the E. coli chromosome [Thelen, P., Tsuchiya, T., and Goldberg, E.B. (1991) J. Bacteriol. 173, 6553-6557]. We found that the NhaB-defective cells cannot grow in a high pH medium. Furthermore, intracellular pH in the mutant cells was almost the same as extracellular pH between 7.9 and 9.1, that is, intracellular pH was not regulated at this pH range. On the other hand, intracellular pH of the wild-type cells was maintained at about 7.6 when the extracellular pH was between 7.6 and 8.5. Thus, the NhaB Na+/H+ antiporter is essential for the regulation of intracellular pH under alkaline conditions in E. coli. Introduction of nhaA gene into the mutant cells increased Na+/H+ antiporter activity, but did not restore the defective growth and defective intracellular pH regulation under alkaline conditions.

The pKa of the protonated Schiff bases of gecko cone and octopus visual pigments

A visual pigment is composed of retinal bound to its apoprotein by a protonated Schiff base linkage. Light isomerizes the chromophore and eventually causes the deprotonation of this Schiff base linkage at the meta II stage of the bleaching cycle. The meta II intermediate of the visual pigment is the active form of the pigment that binds to and activates the G protein transducin, starting the visual cascade. The deprotonation of the Schiff base is mandatory for the formation of meta II intermediate. We studied the proton binding affinity, pKa, of the Schiff base of both octopus rhodopsin and the gecko cone pigment P521 by spectral titration. Several fluorinated retinal analogs have strong electron withdrawing character around the Schiff base region and lower the Schiff base pKa in model compounds. We regenerated octopus and gecko visual pigments with these fluorinated and other retinal analogs. Experiments on these artificial pigments showed that the spectral changes seen upon raising the pH indeed reflected the pKa of the Schiff base and not the denaturation of the pigment or the deprotonation of some other group in the pigment. The Schiff base pKa is 10.4 for octopus rhodopsin and 9.9 for the gecko cone pigment. We also showed that although the removal of Cl- ions causes considerable blue-shift in the gecko cone pigment P521, it affects the Schiff base pKa very little, indicating that the lambda max of visual pigment and its Schiff base pKa are not tightly coupled.

A urease-negative mutant of Helicobacter pylori constructed by allelic exchange mutagenesis lacks the ability to colonize the nude mouse stomach

The urease of Helicobacter pylori has been proposed to be one of its pathogenic factors. A kanamycin resistance determinant was inserted in a cloned urease gene, and transformation-mediated allelic exchange mutagenesis was carried out to introduce the disrupted gene into the corresponding wild-type chromosomal region of a clinical isolate of H. pylori, CPY3401. The resulting mutant, HPT73, had the null activity of urease. Nude mouse stomachs were challenged with these two isogenic strains to examine the role of urease in pathogenesis. Gastritis was found in the CPY3401-challenged stomachs, from which bacteria indistinguishable from CPY3401 were recovered. There was no gastritis in the HPT73-challenged stomachs, and we could not recover H. pylori from them. These results indicated that H. pylori urease is essential for colonizing the nude mouse stomach.

Transcriptional attenuation and differential mRNA stability in the regulation of the Escherichia coli melibiose operon

The organization of the melibiose operon of Escherichia coli is promoter-melA-melB. The amount of the product (alpha-galactosidase) of the first gene (melA) is much larger than that of the product (melibiose permease) of the second gene (melB). Using the chloramphenicol acetyltransferase gene (cat) as reporter, we found that there was an element between melA and melB, which reduced the expression of the downstream gene, melB. This region contained a boxA-like sequence, which is known as a binding site for an attenuation factor, NusA. Northern hybridization analysis revealed that the ratio of melA mRNA and melAB mRNA was comparable with the ratio of the melA and melB products. We also found that the melA mRNA was about 3-fold more stable than the melAB mRNA. Experimental results obtained with a nusAts mutant suggested that the NusA protein is involved in the reduced expression of the melB gene. We conclude that the production ratio of alpha-galactosidase and melibiose permease is regulated at two levels: 1) transcription and 2) mRNA stability.

Characterization of the lactose transport system in Citrobacter freundii

The lactose transport system of Citrobacter freundii was characterized. Both the lactose transport system and beta-galactosidase were induced with either lactose or isopropyl-beta-D-thiogalactopyranoside (IPTG), the latter being the better inducer. The Km values for methyl-beta-D-thiogalactopyranoside (TMG) transport and lactose transport were 0.61 mM and 1.1 mM, respectively, and the Vmax values were 53 nmol/min/mg cell protein and 12 nmol/min/mg cell protein, respectively. Thus, TMG is a better substrate than lactose. Thiogalactopyranoside (TDG) was a very potent competitive inhibitor. Neither Na+ nor Li+ had a significant effect on the TMG transport or the lactose transport. Proton/substrate cotransport (symport) via this system was observed.

Properties of the Na+/H+ antiporter in Vibrio parahaemolyticus

The properties of the Na+/H+ antiporter in Vibrio parahaemolyticus, a slightly halophilic bacterium, were investigated using everted membrane vesicles. It appears that at least two Na+/H+ antiporters are present, one that is pH-dependent and one that is pH-independent. These two antiporters appear to correspond to the NhaA and NhaB antiporters of Escherichia coli, respectively. It seems that amiloride strongly inhibits the pH-dependent antiporter. Na+ is the best substrate for both of the two V. parahaemolyticus antiporters. Li+ is a poorer substrate and K+ is not a substrate. No K+/H+ antiport activity was detected in membrane vesicles of this organism. The Na+(Li+)/H+ antiport activity greatly increased with an increase in pH of the assay medium. pH did not affect the Km value of the Na+/H+ antiport, but it did increase the Vmax.

Enhancement of serine-sensitivity by a gene encoding rhodanese-like protein in Escherichia coli

When cells of Escherichia coli are grown on lactate (or other carbon sources), an addition of serine to the medium causes growth inhibition. This growth inhibition is caused by inhibition by serine of homoserine dehydrogenase I, which is involved in threonine-isoleucine biosynthesis [Hama, H., Sumita, Y., Kakutani, Y., Tsuda, M., & Tsuchiya, T. (1990) Biochem. Biophys. Res. Commun. 168, 1211-1216]. We have cloned and sequenced genes which enhance the serine-sensitivity. Two open reading frames were found and designated as sseA and sseB. Introduction of either sseA or sseB gene, or both, into E. coli cells enhanced the serine-sensitivity. The sseA gene elicited stronger enhancement than sseB. The deduced amino acid sequence of SseA showed considerable similarity with that of bovine liver rhodanese, which catalyzes sulfur transfer from thiosulfate. We observed a twofold increase in rhodanese activity in E. coli cells harboring a plasmid carrying the sseA gene. The position of sseA in the genetic map is around 52'. However, sseA is different from cysM, which codes for O-acetylserine sulfhydrylase-B, an enzyme catalyzing sulfur transfer from thiosulfate to O-acetylserine, the map position of which is also around 52'.

Degradation of polyetherurethane by subcutaneous implantation into rats. I. Molecular weight change and surface morphology

Two kinds of polyetherurethane (PEU), U-3 and U-8, were coated in thin layers on an ethylene-vinylalcohol copolymer (EVAL) film 0.1 mm thick. U-3 is a nonsegmented PEU prepared from 4,4'-diisocyanatodiphenylmethane (MDI) and poly(tetramethylene oxide) of Mn = 1,000 (PTMO 1000), and U-8 is a segmented PEU prepared from MDI, PTMO 1000, and 1,4-butanediol. The coating thicknesses were 0.0068 and 0.022 mm for U-3 and U-8, respectively. These coated films were implanted subcutaneously into rats and retrieved after various weeks. The coatings on the retrieved samples were dissolved in tetrahydrofuran (THF), and the average molecular weight (MW) was determined by injecting the THF solution into a gel permeation chromatograph. In the case of U-3, MW increased after 2 weeks, then decreased over the implantation period. After 10 weeks, U-3 almost disappeared from the base film. In the case of U-8, MW reached the maximum at 4 weeks postimplantation then decreased gradually over the implantation period. The rate and degree of MW change were greater in U-3 than in U-8. Here, we argue that, in the early stage, low molecular weight PTMO/MDI oligomers leached out from the PEUs to the inflammatory exudate to increase MW, and in the later stage macrophage attachment/activation had a role in the degradation of PEUs. The surface morphologic changes observed by scanning electron microscopy are also discussed.

Observation of ganglioside lactone formation with CD spectrometry

Monolactone (NeuAc1-9NeuAc linkage) formation of a ganglioside, GD1b, was observed at 20 degrees C on solutions ranging in concentration from 0.008 to 1.7 mM and in pH from 2 to 8.1, by following the change of ellipicity at 235 nm, where lactonized gangliosides showed a strong Cotton effect. The lactonization was found to be a first-order reaction in both GD1b and H+ in the initial stage but was affected later by a backward reaction, hydrolysis of the lactone linkage. The rate constant was 0.08 h-1 at pH 3. At this pH the reaction went close to equilibrium in 24 h at approximately 70% lactonization. At pH higher than 5.9 no change was observed in the ellipticity within 30 h, suggesting the possibility that at most 0.6% of the ganglioside lactonized. Lactonization of another ganglioside, GD3, in glacial acetic acid was observed with a 0.2-mm cell, agreeing well with a reported result.

Liver fluke infection and cholangiocarcinoma: model of endogenous nitric oxide and extragastric nitrosation in human carcinogenesis

Cancers arising during bacterial, viral and parasitic infection provide useful models to investigate the link between inflammation and carcinogenesis. Because the inflammatory agent is known, relationships between immune responses, the production of DNA-damaging agents, such as nitric oxide, oxygen radicles and N-nitroso compounds, and cancer risk can be explored. This paper first describes the close relationship between infection with the liver fluke, Opisthorchis viverrini, and cholangiocarcinoma in humans. Data are then presented which demonstrate an elevation in levels of salivary nitrite and urinary and plasma nitrate among men with moderate and heavy liver fluke infections compared to uninfected controls which was absent 4 months after the parasites were cleared with praziquantel. Because of the strict control over subject selection and dietary intake plus the absence of the increase following treatment, we conclude that the higher levels of nitrate and nitrite reflect endogenous generation of nitric oxide resulting from liver fluke infection. Excess nitric oxide generation in the inflamed tissue is likely to lead directly to the formation of N-nitroso compounds mediated by activated macrophages. Further work will attempt to demonstrate a link between this increase and both parasite-specific immune responses and the risk of cancer.

Lithium toxicity and Na+(Li+)/H+ antiporter in Escherichia coli

The lithium ion (Li+) shows toxicity against Escherichia coli cells when present in a high concentration in the environment. Since Li+ is extruded from cells via a Na+(Li+)/H+ antiporter, this antiporter must be involved in the detoxification of Li+. Two Na+(Li+)/H+ antiporters (NhaA system and NhaB system) are known to be present in E. coli. We investigated the properties of the antiporters and the participation of these systems in the detoxification of Li+ using mutants lacking one of the antiporters, or lacking both of them. Although the affinity for Li+ of the two systems was almost the same, the Vmax value for Li+ transport of the NhaA system was about 12 times larger than that of the NhaB system. Wild type cells were unable to grow in the presence of 0.7 M LiCl. Although a wild type cell and a mutant lacking the NhaB system grew in the presence of 0.6 M LiCl, a mutant lacking the NhaA system did not. This second mutant grew in the presence of 0.1 to 0.2 M LiCl. A mutant lacking both the NhaA and NhaB systems could not grow in the presence of 30 mM LiCl.

Long-term survival in a patient with malignant carcinoid treated with high-dose octreotide

Octreotide acetate, a long-acting somatostatin analogue, is effective in controlling and markedly reducing the symptoms of carcinoid crisis. We report a patient with carcinoid syndrome with prolonged survival for 4.5 years with high dose octreotide therapy and survived for 7.5 years after the first flushing, in spite of episodes of severe carcinoid crisis. Dose escalation was required in order to control carcinoid symptoms, and the final dosage was 5,950 micrograms/day. Although administration of such a high dosage of octreotide has never been reported before, we found that octreotide could be used at this dosage safely without inducing serious side effects, and probably prolonged the patient's survival. Our experience with this case indicates that octreotide acetate is an effective drug in controlling carcinoid crisis and prolonging survival without serious side effects.

Limited diffusibility of gene products directed by a single nucleus in the cytoplasm of multinucleated myofibres

Two types of beta-galactosidase genes, whose products are distributed in the nucleus (N beta-gal) or cytoplasm (C beta-gal), were injected with fructose intramuscularly into the quadriceps of adult mice. Regionally restricted and overlapped distributions of both gene products were observed in the myofibres. These findings indicate that N beta-gal is incorporated into the nucleus responsible for its synthesis and that C beta-gal becomes located in the vicinity of the nucleus after its synthesis. This restricted location of C beta-gal in myofibres remained unchanged during the development of infant mouse muscle. Thus, the gene products directed by the nucleus of myofibres seem to show limited diffusibility, suggesting a universal localization of subcellular domains in myofibres.

Tissue characterization of pneumonia and irradiated rat lungs with magnetic resonance relaxation times

To interpret the MRI signal intensities, the T1 and T2 values were determined in vitro for rat lungs with radiation pneumonitis, fibrosis or pneumonia, and also for muscle and fat tissues. The transverse magnetization decays mentioned above exhibited two components, a T2 fast (T2f) and a T2 slow (T2s) component. Lungs from rats with pneumonia had significantly longer T2f and T2s values than lungs from rats with radiation pneumonitis and fibrosis. The T2f and T2s values for a "pneumonia lung" were not significantly different from those of muscle. The measured values of T2f and T2s suggested that radiation pneumonitis and fibrosis likely exhibit lower signal intensities than do muscle and that a "pneumonia lung" likely exhibits a similar signal intensity to that of muscle on T2-weighted MR images.

Identification and characterization of a new plasmid carrying genes for degradation of 2,4-dichlorophenoxyacetate from Pseudomonas cepacia CSV90

Pseudomonas cepacia CSV90 is able to utilize 2,4-dichlorophenoxyacetate (2,4-D) and 2-methyl-4-chlorophenoxyacetate as sole sources of carbon and energy. Mutants of the strain CSV90 which had lost this ability appeared spontaneously on a nonselective medium. The wild-type strain harbored a 90-kb plasmid, pMAB1, whereas 2,4-D-negative mutants either lost the plasmid or had a 70-kb plasmid, pMAB2. The plasmid pMAB2 was found to have undergone a deletion of a 20-kb fragment of pMAB1. The plasmid-free mutants regained the ability to degrade 2,4-D after introduction of purified pMAB1 by electroporation. Cloning in Escherichia coli of a 10-kb BamHI fragment from pMAB1, the region absent in pMAB2, resulted in the expression of the gene tfdC encoding 3,5-dichlorocatechol 1,2-dioxygenase. After subcloning, the tfdC gene was located in a 1.6-kb HindIII fragment. The nucleotide sequence of the tfdC gene and the restriction map of its contiguous region are identical to those of the well-characterized 2,4-D-degradative plasmid pJP4 of Alcaligenes eutrophus, whereas the overall restriction maps of the two plasmids are different. The N-terminal 44-amino-acid sequence of the enzyme purified from the strain CSV90 confirmed the reading frame in the DNA sequence for tfdC and indicated that the initiation codon GUG is read as methionine instead of valine.

Potentiation of physical dependence on diazepam by ondansetron in rats

The effects of ondansetron, a 5-HT3 antagonist, on the development of physical dependence on diazepam were examined in rats using a drug-admixed food method. Rats were treated with diazepam or diazepam in combination with ondansetron for 26 days. After an abrupt withdrawal from diazepam, the incidence of withdrawal signs, such as jerks, tremors and convulsions, and withdrawal scores, were potentiated by co-administration of ondansetron. On the other hand, rats which had been treated with ondansetron alone for 33 days did not show any withdrawal signs after abrupt withdrawal from ondansetron. These findings suggest that ondansetron does not possess physical dependence liability, but does potentiate the development of physical dependence on diazepam. Regulation of serotonergic neurons through 5-HT3 receptors may affect the development of physical dependence on diazepam.

A mutagenesis system utilizing a Tn1722 derivative containing an Escherichia coli-specific vector plasmid: application to Pseudomonas species

A novel transposon (Tn) mutagenesis system for Gram- non-enteric bacteria was developed which allowed rapid and one-step cloning of the mutated region in Escherichia coli. The Tn constructed was Tn1722-299Km, a Tn1722 derivative containing a KmR gene and the entire sequence of an E. coli-specific plasmid, pACYC184. The hybrid plasmid consisting of Tn1722-299Km and the transfer genes of plasmid R388 was conjugally transferred from E. coli to Pseudomonas putida or P. aeruginosa, and selection of the transconjugants expressing the Tn-specified resistance genes led to isolation of insertion mutants of the recipient strain. The presence of the pACYC184 replicon in the Tn greatly facilitated rapid and easy cloning of the mutated region in E. coli through (i) mini-scale preparation of the genomic DNA from the Tn-inserted mutant, (ii) digestion of the DNA with an appropriate restriction endonuclease, (iii) self-ligation, and (iv) transformation of E. coli to recover the plasmid carrying the Tn-specified resistance marker. This procedure was successfully adapted to clone the Tn-inserted trpBA region of P. putida. Such a cloned region was further employed to isolate the wild-type allele of the trpBA region without construction of a genomic library.