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Biomedical subjects

H Himeno

Publications and source records attributed to H Himeno.

At least 19 recordsLinked to original sources
PubMed1999

Functional and structural analysis of a pseudoknot upstream of the tag-encoded sequence in E. coli tmRNA.

Escherichia coli tmRNA (transfer-messenger RNA) facilitates a trans-translation reaction in which a stalled ribosome on a terminatorless mRNA switches to an internal coding sequence in tmRNA, resulting in the addition of an 11 amino acid residue tag to the truncated protein that is a signal for degradation and in recycling of the stalled ribosome. A tmRNA secondary structure model with a partial tRNA-like structure and several pseudoknots was recently proposed. This report describes an extensive mutational analysis of one predicted pseudoknot (PK1) located upstream of the E. coli tmRNA tag-encoded sequence. Both the extent of aminoacylation and the alanine incorporation into the tag sequence, reflecting the two functions of tmRNA, were measured in vitro for all the engineered RNA variants. To characterize structure-function relationships for the tmRNA mutants, their solution conformations were investigated by using structural probes and by measuring the temperature dependence of their UV absorbance. This analysis strongly supports the presence of a pseudoknot in E. coli tmRNA, and its involvement in trans-translation. Mutations disrupting the first stem of the pseudoknot inactivate function and promote stable alternative conformations. Mutations of the second stem of the pseudoknot also effect both functions. The nucleotide stretch between the two stems (loop 2) is required for efficient trans-translation, and nucleotides at positions 61 and 62 must be guanine residues. The probing data suggest the presence of magnesium ion(s) interacting with loop 2. The loops crossing the minor and major grooves can be mutated without significant effects on tmRNA function. Nucleotide insertion or deletion between the pseudoknot and the coding sequence do not change the mRNA frame of the tag-peptide sequence, suggesting that the pseudoknot structure is not a determinant for the resumption of translation.

Alanine↗
PubMed1998

Cross-species aminoacylation of tRNA with a long variable arm between Escherichia coli and Saccharomyces cerevisiae.

Prokaryotes have three amino acid-specific class II tRNAs that possess a characteristic long variable arm, tRNASer, tRNALeuand tRNATyr, while eukaryotes have only two, tRNASerand tRNALeu. Because of such a phylogenetic divergence in the composition of tRNA, the class II tRNA system is a good candidate for studying how the tRNA recognition manner has evolved in association with the evolution of tRNA. We report here a cross-species aminoacylation study of the class II tRNAs, showing the unilateral aminoacylation specificity between Escherichia coli and a yeast, Saccharomyces cerevisiae. Both SerRS and LeuRS from E.coli were unable to aminoacylate yeast class II tRNAs; in contrast, the yeast counterparts were able to aminoacylate E.coli class II tRNAs. Yeast seryl-tRNA synthetase was able to aminoacylate not only E.coli tRNASerbut also tRNALeuand tRNATyr, and yeast LeuRS was able to aminoacylate not only E.coli tRNALeubut also tRNATyr. These results indicate that the recognition manner of class II tRNA, especially the discrimination strategy of each aminoacyl-tRNA synthetase against noncognate class II tRNAs, is significantly divergent between E.coli and yeast. This difference is thought to be due mainly to the different composition of class II tRNAs in E.coli and yeast.

Acylation↗
PubMed1998

Presence and location of modified nucleotides in Escherichia coli tmRNA: structural mimicry with tRNA acceptor branches.

Escherichia coli tmRNA functions uniquely as both tRNA and mRNA and possesses structural elements similar to canonical tRNAs. To test whether this mimicry extends to post-transcriptional modification, the technique of combined liquid chromatography/ electrospray ionization mass spectrometry (LC/ESIMS) and sequence data were used to determine the molecular masses of all oligonucleotides produced by RNase T1 hydrolysis with a mean error of 0.1 Da. Thus, this allowed for the detection, chemical characterization and sequence placement of modified nucleotides which produced a change in mass. Also, chemical modifications were used to locate mass-silent modifications. The native E.coli tmRNA contains two modified nucleosides, 5-methyluridine and pseudouridine. Both modifications are located within the proposed tRNA-like domain, in a seven-nucleotide loop mimicking the conserved sequence of T loops in canonical tRNAs. Although tmRNA acceptor branches (acceptor stem and T stem-loop) utilize different architectural rules than those of canonical tRNAs, their conformations in solution may be very similar. A comparative structural and functional analysis of unmodified tmRNA made by in vitro transcription and native E.coli tmRNA suggests that one or both of these post-transcriptional modifications may be required for optimal stability of the acceptor branch which is needed for efficient aminoacylation.

Base Composition↗
PubMed1998

Cough-challenge trial with a new angiotensin-converting enzyme inhibitor, imidapril.

This study was conducted to examine whether imidaprilat, an active diacid of the angiotensin-converting enzyme (ACE) inhibitor imidapril, preferentially inhibits angiotensin I degradation rather than bradykinin degradation, and whether imidapril is less active than other ACE inhibitors in inducing cough in patients with hypertension. The effect of imidaprilat on the inhibition of pressor response to angiotensin I and augmentation of depressor response to bradykinin was compared with that of enalaprilat and captopril in anesthetized rats. To determine the incidence of cough associated with imidapril, patients with a history of ACE inhibitor-induced dry cough were enrolled in a randomized, open-labeled, crossover trial with two 6-week periods to be treated with imidapril or amlodipine, a calcium-channel blocker. The recurrence of cough was assessed during both treatments. In the animal study, there were no significant differences in the ratio of inhibition of pressor response to angiotensin I and the augmentation of depressor response to bradykinin among the ACE inhibitors. In the cough-challenge trial, a total of 60 patients with hypertension were enrolled in the study. Cough and cough related symptoms recurred in 98.3% of the patients (59/ 60) during imidapril therapy. In contrast, only two patients reported cough during treatment with amlodipine. These results indicate that imidapril has no selectivity in inhibiting angiotensin I- and bradykinin-degradation in rats, and that clinically it is not different from other ACE inhibitors in inducing cough in patients with hypertension.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1998

A bacterial RNA that functions as both a tRNA and an mRNA.

Bacterial tmRNA (transfer-messenger RNA, also known as 10Sa RNA) contains a tRNA-like structure in the 5'- and 3'-end sequences and an internal reading frame encoding a 'tag' peptide. The dual function of this molecule as both a tRNA and an mRNA facilitates a trans-translation reaction, in which a ribosome can switch between translation of a truncated mRNA and the tmRNA's tag sequence. The result is a chimeric protein with the tag peptide attached to the C-terminus of the truncated peptide.

Base Sequence↗
PubMed1998

Primary structures of hemagglutinin-esterase and spike glycoproteins of murine coronavirus DVIM.

Diarrhea virus of infant mice (DVIM) is a member of murine hepatitis viruses (MHVs). The nucleotide sequences of the genes encoding the hemagglutinin-esterase (HE) and the spike (S) glycoproteins from DVIM were determined and compared with those of other MHVs. The deduced amino acid sequence of the HE protein was most similar to that of MHV-S strain (94% identity), and the S protein sequence was most similar to that of MHV-Y strain (90% identity). The DVIM HE protein has a unique N-linked glycosylation site in addition to other glycosylation sites common to many MHV strains. Unlike in some typical MHV strain, such as MHV-A59 and MHV-JHM, the vast majority of the S glycoprotein molecules in DVIM exist an uncleaved form probably due to several amino acid substitutions around the cleavage site.

Amino Acid Sequence↗
PubMed1997

Development of hepatic sinusoidal structure with special reference to the Ito cells.

To elucidate sinusoidal cell structure and function under normal conditions and their behavior in diseased settings, an understanding of their developmental aspects is needed. At day 10 of gestation in mice and rats or at 5 weeks of gestation in humans, the hepatic cords grow into the mesenchymal tissue of the septum transversum, and the primitive sinusoidlike structure is simultaneously observed between the liver cell cords. In the margin of the growing liver primordium, mesenchymal cells in the septum transversum are trapped in the subendothelial space. These subendothelial cells are at the early stages of organogenesis and become progenitors of the Ito cells. By days 12-14 of gestation in mice and rats or 8 weeks of gestation in humans, the basic structure of the sinusoids has developed. Embryonic hepatic sinusoids are usually lined by a continuous endothelium without basement membranes, and an incompletely fenestrated sinusoid appears at the middle gestational stage. In the late gestational stages, the Ito cells exhibit myofibroblastlike features in humans, mice, and rats. In association with this event, perisinusoidal reticular networks are gradually intensified. After birth until days 4-5 in mice and rats, the sinusoidal and perisinusoidal structures are almost completely formed, although slight morphological differences from those in adult livers still exist. What happens to sinusoidal endothelial cells and Ito cells in hepatic fibrosis-cirrhosis of the adult may be a deviated or uncontrolled occurrence of what goes on during the fetal period, i.e., a continuous nonfenestrated sinusoidal lining in the early embryonic stage and a myofibroblastlike transformation of Ito cells in late fetal life.

Animals↗
PubMed1997

In vitro trans translation mediated by alanine-charged 10Sa RNA.

10Sa RNA is a bacterial small stable RNA, in which the 5' and 3'-terminal sequences can be folded into a tRNA-like secondary structure which can be aminoacylated with alanine. It was found that Escherichia coli 10Sa RNA facilitated the incorporation of alanine, tyrosine, aspartic acid and glutamic acid, but not valine, isoleucine, serine or arginine, into the growing polypeptide in vitro, depending on poly (U)-directed poly-phenylalanine synthesis. This result indicates that 10Sa RNA functions as an mRNA for the tag-peptide which has been found to be attached to the C termini of truncated polypeptides synthesized in vivo. Aminoacylation with alanine was required for tag-specific amino acid incorporation and for efficient association of 10Sa RNA with the ribosome, indicating that 10Sa RNA also functions as an alanine tRNA in the tag-peptide synthesis. The dual function of 10Sa RNA both as an mRNA and as a tRNA in vitro strongly supports the trans translation hypothesis.

Alanine↗
PubMed1997

Only one nucleotide insertion to the long variable arm confers an efficient serine acceptor activity upon Saccharomyces cerevisiae tRNA(Leu) in vitro.

Several tRNA species have a long variable arm composed of over ten nucleotides, which are relevant to those specific to serine, leucine and tyrosine in prokaryotes, while there are only serine and leucine-specific tRNAs in eukaryotes. To clarify the evolutionary aspects of the identity determination mechanism of these tRNAs, the tRNA(Ser) recognition in Saccharomyces cerevisiae was studied. Unmodified tRNA(Leu) transcript had serylation ability of low efficiency, but native tRNA(Leu) did not, indicating that some modification of tRNA(Leu) serves as a negative identity determinant for seryl-tRNA synthetase. Changing the discriminator base did not seriously affect the serine accepting efficiency. The tRNA(Leu) transcript possessing the variable arm of tRNA(Ser) was efficiently aminoacylated with serine. Eventually, it was found that only one nucleotide insertion to the variable arm of tRNA(Leu) was sufficient to confer an efficient serine accepting activity. The mode of serine tRNA recognition is similar to that in Escherichia coli in that the end of the long variable arm, but not the anticodon or discriminator base, is important. However, S. cerevisiae seryl-tRNA synthetase adopts a substantially different mechanism for rejection of tRNA(Leu) from that of its E. coli counterpart.

Base Sequence↗
PubMed1997

Fosinopril. Clinical pharmacokinetics and clinical potential.

Fosinopril is a phosphorus-containing ester prodrug of an angiotensin-converting enzyme (ACE) inhibitor. It is hydrolysed mainly in the gastrointestinal mucosa and liver to the active diacid, fosinoprilat, which has unique pharmacological properties. The majority of the active moieties of other ACE inhibitors are excreted in the urine. This means that an adjustment in either the dosage and/or the administration interval is needed in patients with moderate to severe renal dysfunction, in order to reduce drug accumulation and the possibility of an excessive decrease in blood pressure or other adverse effects. On the other hand, fosinoprilat is excreted both in urine and bile (as with temocaprilat, zofenoprilat and spiraprilat), and thus an adjustment of dosage and/or administration interval may be unnecessary in patients with moderate to severe renal dysfunction, as impaired renal function influences little of the pharmacokinetics of fosinoprilat. Furthermore, the available evidence suggests that the pharmacokinetic variables of fosinoprilat in patients receiving haemodialysis were similar to those in patients with moderate to severe renal dysfunction. Dosage modifications or supplemental dose administration following dialysis may be unnecessary. The hypotensive effect of the combination of fosinopril and a diuretic is synergistic. Pharmacokinetic interactions with fosinopril are unlikely in patients receiving thiazide or loop diuretics. Fosinopril has beneficial effects for patients with hypertension and left ventricular hypertrophy because it produces an adequate reduction in blood pressure and reversal of left ventricular hypertrophy. There are a large number of studies of the pharmacokinetics of fosinopril. However studies of its pharmacokinetic drug interactions with other drugs are far fewer. Further investigations are needed in several clinical settings.

Absorption↗
PubMed1997

Probing the structure of the Escherichia coli 10Sa RNA (tmRNA).

The conformation of the Escherichia coli 10Sa RNA (tmRNA) in solution was investigated using chemical and enzymatic probes. Single- and double-stranded domains were identified by hydrolysis of tmRNA in imidazole buffer and by lead(II)-induced cleavages. Ribonucleases T1 and S1 were used to map unpaired nucleotides and ribonuclease V1 was used to identify paired bases or stacked nucleotides. Specific atomic positions of bases were probed with dimethylsulfate, a carbodiimide, and diethylpyrocarbonate. Covariations, identified by sequence alignment with nine other tmRNA sequences, suggest the presence of several tertiary interactions, including pseudoknots. Temperature-gradient gel electrophoresis experiments showed structural transitions of tmRNA starting around 40 degrees C, and enzymatic probing performed at selected temperatures revealed the progressive melting of several predicted interactions. Based on these data, a secondary structure is proposed, containing two stems, four stem-loops, four pseudoknots, and an unstable structural domain, some connected by single-stranded A-rich sequence stretches. A tRNA-like domain, including an already reported acceptor branch, is supported by the probing data. A second structural domain encompasses the coding sequence, which extends from the top of one stem-loop to the top of another, with a 7-nt single-stranded stretch between. A third structural module containing pseudoknots connects and probably orients the tRNA-like domain and the coding sequence. Several discrepancies between the probing data and the phylogeny suggest that E. coli tmRNA undergoes a conformational change.

Alanine↗
PubMed1997

Escherichia coli tmRNA (10Sa RNA) in trans-translation.

Here we show that Escherichia coli tmRNA (10Sa RNA) has a dual function both as an mRNA and as a tRNA in vitro. The function as a tRNA is prerequisite for the function as an mRNA. These observations strongly support the trans-translation hypothesis.

Amino Acid Sequence↗
PubMed1997

Recognition system of class II tRNA in Escherichia coli and yeast.

The recognition system of class II tRNA, tRNA(Ser) and tRNA(Leu), in a yeast Saccharomyces cerevisiae was studied using T7 RNA polymerase transcription system. Yeast SerRS recognizes the long variable arm as in E. coli. However, the anticodon loop of tRNA(Leu), which has no effect on leucylation in E. coli, play a key role for recognition by LeuRS. Results suggest that the recognition style of yeast class II tRNA is substantially different from that of E. coli.

Escherichia coli↗
PubMed1996

Interaction of 10Sa RNA with ribosomes in Escherichia coli.

10Sa RNA is a bacterial small stable RNA, in which the 5'- and 3'-end sequences are folded into a tRNA-like structure. The RNA accepts alanine in vitro, and interacts with 70S ribosomes in the cells. In this study, we examined the ribosome-binding properties of Escherichia coli 10Sa RNA in vivo, and found that the aminoacylation ability of 10Sa RNA with alanine is necessary for the binding to 70S ribosomes. 10Sa RNA was also found to bind only to 70S monosomes and not to polysomes. Recently, E. coli 10Sa RNA was suggested to be used as mRNA for tag peptides, which were found to attach to the C-termini of truncated peptides synthesized in vivo. The present results are consistent with the 'trans-translation' model, which has been proposed for tag-peptide synthesis.

Escherichia coli↗
PubMed1996

The anticodon loop is a major identity determinant of Saccharomyces cerevisiae tRNA(Leu).

The recognition of tRNALeu, one of the class II tRNAs having a long variable arm, by leucyl-tRNA synthetase in Saccharomyces cerevisiae was studied using the T7 transcription system. Exchanging the anticodon arm of tRNALeu but not the D- or T psi C-arm to that of tRNASer seriously affected the leucine accepting activity. Two nucleotides in the anticodon loop, A35 and G37, were found to be important for leucylation. It was also found that the discriminator base, A73, is required for leucylation, and G73 of tRNASer functions as a negative identity determinant for leucyl-tRNA synthetase. Introducing a set of three base substitutions at positions 35, 37 and 73 was sufficient to convert tRNASer into an efficient leucine acceptor. These results indicate that the identity elements of tRNALeu lie at the second position of the anticodon and the 3' adjacent to the anticodon as well as the discriminator position. Such a sequence specific recognition manner is significantly different from that of Escherichia coli, in which not the anticodon but the tertiary structural elements play a key role in discriminating from other class II tRNAs. The leucine system is the first example which shows that the requirement of the anticodon sequence is variable among species.

Anticodon↗
PubMed1996

Structural organization of Escherichia coli tmRNA.

A secondary structure of Escherichia coli 10Sa RNA (tmRNA) recently proposed on the basis of a variety of chemical and enzymatic probing data combined with phylogenetic analysis (Felden et al, in press), indicates a highly folded structure. Several long-range interactions including pseudoknots are proposed based on comparative analysis of 10 tmRNA genes. Whereas most of the probing data support these predicted secondary structures, several atypical reactivities in specific domains of the molecule suggest structural dynamics, perhaps relating to the complex functions of the molecule as both tRNA and mRNA. The structure of tmRNA has three modular units; a tRNA-like domain, an mRNA-like domain and an intricate connecting unit probably responsible for correct orientation of the two functional parts of the molecule.

Base Sequence↗