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H Himeno

Publications and source records attributed to H Himeno.

At least 19 recordsLinked to original sources
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↗
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↗
PubMed1995

Identity elements of Saccharomyces cerevisiae tRNA(His).

Recognition of tRNA(His) by Saccharomyces cerevisiae histidyl-tRNA synthetase was studied using in vitro transcripts. Histidine tRNA is unique in possessing an extra nucleotide, G-1, at the 5' end. Mutation studies indicate that this irregular secondary structure at the end of the acceptor stem is important for aminoacylation with histidine, while the requirement of either base of this extra base pair is smaller than that in Escherichia coli. The anticodon was also found to be required for histidylation. The regions involved in histidylation are essentially the same as those in E.coli, whereas the proportion of the contributions of the two portions distant from each other, the anticodon and the end of the acceptor stem, makes a substantial difference between the two systems.

Acylation↗
PubMed1995

Sequential changes in human Ito cells and their relation to postnecrotic liver fibrosis in massive and submassive hepatic necrosis.

To examine the relationship of Ito cells to postnecrotic liver fibrosis, liver specimens, obtained at autopsy from 17 patients with acute massive necrosis (AMN) and acute submassive hepatic necrosis (ASMN), were examined immunohistochemically. In normal adult livers, Ito cells positive for alpha-smooth muscle actin isoform (ASMA) were rarely seen, scattered along hepatic sinusoids. In contrast, in AMN the Ito cells in necrotic areas became strongly positive for ASMA. They were swollen with elongated cytoplasmic processes along collapsed sinusoidal walls. Around these ASMA-positive Ito cells, there were numerous infiltrated macrophages and lymphocytes present. There was no significant alteration of fibroblasts in the portal tracts. In the middle and late stages of ASMN, the spindle-shaped ASMA-positive Ito cells formed a continuous cellular network. New fibre formation was predominantly around them. In this immediate postnecrotic fibrosis, ASMA-positive stromal cells of Ito cell origin were distributed irregularly and were closely associated with reticulin and newly-formed collagen fibres. Regenerative nodules were surrounded by dense layers of ASMA-positive stromal cells. Throughout the stages of ASMN, portal fibroblasts remained negative for ASMA. We believe that Ito cells in necrotic areas show myofibroblastic transformation and play a central role in the postnecrotic liver fibrosis. Portal fibroblasts play no significant part in this type of fibrosis.

Actins↗
PubMed1995

Nucleotide sequence and gene organization of the starfish Asterina pectinifera mitochondrial genome.

The 16,260-bp mitochondrial DNA (mtDNA) from the starfish Asterina pectinifera has been sequenced. The genes for 13 proteins, two rRNAs and 22 tRNAs are organized in an extremely economical fashion, similar to those of other animal mtDNAs, with some of the genes overlapping each other. The gene organization is the same as that for another echinoderm, sea urchin, except for the inversion of a 4.6-kb segment that contains genes for two proteins, 13 tRNAs and the 16S rRNA. Judging from the organization of the protein coding genes, mammalian mtDNAs resemble the sea urchin mtDNA more than that of the starfish. The region around the 3' end of the 12S rRNA gene of the starfish shows a high similarity with those for vertebrates. This region encodes a possible stem and loop structure; similar potential structures occur in this region of vertebrate mtDNAs and also in nonmitochondrial small subunit rRNA. A similar stem and loop structure is also found at the 3' end of the 16S rRNA genes in A. pectinifera, in another starfish Pisaster ochraceus, in vertebrates and in Drosophila, but not in sea urchins. The full sequence data confirm the presumption that AGA/AGG, AUA and AAA codons, respectively, code for serine, isoleucine, and asparagine in the starfish mitochondria, and that AGA/AGG codons are read by tRNA(GCUSer), which possesses a truncated dihydrouridine arm, that was previously suggested from a partial mtDNA sequence. The structural characteristics of tRNAs and possible mechanisms for the change in the mitochondrial genetic code are also discussed.

Amino Acid Sequence↗
PubMed1995

Similarities and differences in tRNA identity between Escherichia coli and Saccharomyces cerevisiae: evolutionary conservation and divergence.

Identity elements, which allow correct recognition of tRNAs by their cognate aminoacyl-tRNA synthetase, have been well elucidated in Escherichia coli to begin to see a pattern for tRNA recognition. We examined the identity elements of several tRNA species from Saccharomyces cerevisiae and Thermus thermophilus using in vitro transcripts. Comparison of identity elements among different organisms indicates not only conservation but also evolutionary divergence of tRNA recognition.

Amino Acyl-tRNA Synthetases↗
PubMed1994

Role of the CCA terminal sequence of tRNA(Val) in aminoacylation with valyl-tRNA synthetase.

All known tRNAs have a universal CCA sequence at the 3'-terminal. To study the role of this terminal sequence in the aminoacylation process, base substitutions were introduced into a transcript of Escherichia coli valine tRNA and the effects on the aminoacylation activity with valyl-tRNA synthetase were evaluated. Substitution of the terminal adenosine residue at position 76 by C or U caused a 5-7-fold decrease of valine charging activity in Vmax/Km, while substitution by G resulted in about a 300-fold decrease. In addition, these mutations gave rise to an appreciable level of misaminoacylation with threonine. ATP hydrolysis activity during threonylation was lower in the terminal adenosine mutants than in the wild-type. Mutations introduced at positions 75 and 74 also caused threonylation instead of reducing valylation, albeit to a much smaller extent. These results indicate that the CCA sequence, especially the base portion of the terminal adenosine residue, plays an important role not only in amino-acylation efficiency with valine but also in preventing misaminoacylation by hydrolyzing misactivated threonyl-tRNA(Val).

Acylation↗
PubMed1994

tRNA-like structures in 10Sa RNAs of Mycoplasma capricolum and Bacillus subtilis.

The stable RNAs, whose sequences are homologous to 10Sa RNA of Escherichia coli, have been isolated from Mycoplasma capricolum and Bacillus subtilis, both belonging to the Gram-positive bacterial group. The total nucleotide sequences of the RNAs have been determined by partial RNA sequencing and DNA sequencing of their genes. A comparison of the sequences, together with those of other bacterial 10Sa RNAs so far known, has shown that the 5'- and 3'-end sequences are well conserved among species, while the central parts reveal little homologies. Unexpectedly, the conserved 5'- and 3'-regions can be folded in a common tRNA-like structure containing an amino acid-acceptor stem and a T phi C-stem/loop. The 3'-terminal CCA sequence of B.subtilis 10Sa RNA is not encoded on the DNA, but is added after transcription. Furthermore, the RNA is aminoacylatable with alanine in vitro, and binds to the 70S ribosome in vivo.

Acylation↗
PubMed1994

Escherichia coli seryl-tRNA synthetase recognizes tRNA(Ser) by its characteristic tertiary structure.

To investigate the sequence requirements of Escherichia coli tRNA(Ser) for recognition by seryl-tRNA synthetase, various mutants of unmodified tRNA(Ser) were constructed. Substitution of G2.C71 by C2.G71, but not by A2.U71 or U2.A71, impaired the serine-accepting activity, indicating that this position is not involved in recognition by seryl-tRNA synthetase, but contributes to discrimination from other tRNAs processing C2.G71 such as tRNA(Leu). Other nucleotides characteristic of tRNA(Ser), including the discriminator base, were not involved in recognition by seryl-tRNA synthetase. The anticodon was not involved, as suggested by its sequence variety within the isoacceptors. The long variable arm composed of over ten nucleotides, which is a characteristic feature of tRNA(Ser) together with tRNA(Leu) and tRNA(Tyr), was stem-length-specifically, but not sequence-specifically, important for recognition. In order to introduce a sufficient serine-accepting activity to a tRNA(1LEU) transcript in vitro, besides the change from C2.G71 to G2.C71, the following elements had to be changed to those characteristic of tRNA(Ser): the sequence in the D-loop, the stem pairing pattern of the variable arm, the tertiary base-pair 15.48 and the nucleotide at position 59 in the T psi C-loop. None of the nucleotides at these changed positions was involved in base-specific recognition, indicating that seryl-tRNA synthetase selectively recognizes tRNA(Ser) on the basis of its characteristic tertiary structure rather than the nucleotides specific to tRNA(Ser).

Base Sequence↗
PubMed1994

Hitherto unrecognized arterioles within hepatocellular carcinoma.

The distribution of blood vessels in human hepatocellular carcinoma was studied with the anti-a-smooth muscle actin monoclonal antibody by light and electron microscopy, and with morphometric analysis. a-Smooth muscle actin-positive arterioles were never observed in lobules or pseudolobules of non-cancerous areas, but were frequently seen within hepatocellular carcinomas. Morphometric analysis revealed that most of these arterioles measured between 10 and 25 microns in diameter. The morphology of intratumoural arterioles differed considerably from that of conventional arteries in the portal tracts of the non-cancerous area. The presence of abundant intratumoural arterioles can explain the angiographic hypervascularity of hepatocellular carcinoma and provides a pathological basis for its susceptibility to hypoxia and for arterial embolization as a therapeutic strategy.

Adult↗
PubMed1994

Immunoelectron microscopic observations on Leu-7 positive cells in virus-related chronic liver diseases.

We investigated the liver biopsies of 78 patients with hepatitis virus-related chronic liver diseases (B type; 14 patients, C type; 64 patients) by immunoelectron microscopy with the Leu-7 monoclonal antibody in order to determine the association of NK/K cells in virus-related chronic liver diseases. Most Leu-7 positive cells in the liver had the Pit cell morphology but a few Pit cells were Leu-7 negative. A few Leu-7 positive cells had neither Pit cell nor typical T cell morphology. No ultrastructural difference was observed in Leu-7 positive cells between hepatitis B virus- and hepatitis C virus-related chronic liver diseases. Regardless of virus type and hepatitis activity, the fine morphology of extravascular Leu-7 positive cells differed considerably from intravascular cells. Leu-7 positive cells were regularly seen in the cellular infiltrates but the ratio of Leu-7 positive cells/whole infiltrates was low. There was no correlation between the inflammatory activity of the disease and the level of Leu-7 positive cell infiltration. A virus aetiology (hepatitis-C or hepatitis-B) did not affect Leu-7 positive cell infiltration. We conclude that NK cells play only a small role in the pathogenesis of hepatitis B virus or hepatitis C virus-related hepatocytolysis, during the chronic stage.

Adult↗
PubMed1994

Immunohistochemical identification of Ito cells and their myofibroblastic transformation in adult human liver.

To identify Ito cells in normal and pathological adult human livers, immunohistochemical studies were performed by the avidin-biotin-peroxidase complex method using monoclonal antibodies for alpha-smooth muscle actin (ASMA), desmin, and vimentin. Fifty one needle biopsies, 7 surgically resected specimens, and 5 autopsy specimens were studied. In the normal adult liver vascular smooth muscle cells and pericytes, together with perisinusoidal cells with thin cytoplasmic processes were positive for ASMA. These latter cells formed a loose and discontinuous layer along the sinusoidal walls. Immunoelectron microscopy showed that the ASMA-positive perisinusoidal cells were Ito cells containing fat droplets. The other sinusoidal lining cells were negative for ASMA. In chronic liver disease, ASMA-positive Ito cells showed an increase in number, size, and the intensity of immunostaining in areas of piece-meal necrosis), and formed a continuous cellular network. These cells were dendritic in shape with irregularly elongated cytoplasmic processes and contained an increased amount of microfilaments, in association with loss of the characteristic fat droplets. Thus, their ultrastructural features corresponded to those of myofibroblastic cells. Ito cells showed no staining for desmin in both normal and pathological livers. These results indicate that immunohistochemistry using an anti-ASMA antibody is a sensitive and reliable method for the identification of both normal and transformed Ito cells in adult human livers.

Actins↗
PubMed1994

Alpha-smooth muscle actin-positive perisinusoidal stromal cells in human hepatocellular carcinoma.

The purpose of this study is to clarify the morphological characteristics and functional significance of the perisinusoidal stromal cells in hepatocellular carcinoma. The liver specimens surgically resected from 24 patients with hepatocellular carcinoma were studied by electron microscopy and immunohistochemistry using monoclonal antibodies against alpha-smooth muscle actin, vimentin and desmin. In the tissue space between endothelial cells and trabeculae of cancer cells, the stromal cells were frequently found. They were strongly positive for alpha-smooth muscle actin, weakly and less frequently positive for vimentin but negative for desmin. They varied in shape, size and distribution, stretching cytoplasmic processes and occasionally surrounding the trabeculae of cancer cells. They contained considerable amounts of microfilaments that were positive for alpha-smooth muscle actin and condensed in cell periphery. Along the cell membrane, the short dense areas and pinocytotic vesicles were seen. The external lamina incompletely invested the stromal cells. They were always surrounded by amorphous material. In the granulation tissue and fibrotic areas around necrotic cancer tissue, they were increased in size and number. On the other hand, immunohistochemically and ultrastructurally, they closely resembled the Ito cells in the piecemeal necrosis that showed myofibroblastic transformation. These results suggest that the perisinusoidal stromal cells in nonnecrotic cancer tissue produce the extracellular matrix in the tissue space and maintain the cancerous trabecular structure. After necrosis of cancer tissue, they may become activated and actively participate in the fibrosis.

Actins↗
PubMed1994

Susceptibility to neonatal streptozotocin-induced diabetes in spontaneously hypertensive rats.

We studied the difference in the susceptibility to neonatal streptozotocin (STZ) diabetes between spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY). Two-day-old female SHR and WKY were injected intraperitoneally with 75.0 mg/kg of STZ or vehicle for control. Hyperglycemia developed in both strains at 4 days of age, but SHR were more hyperglycemic. Overt hyperglycemia developed in SHR with aging after a partial recovery from initial hyperglycemia at 10 days of age, whereas WKY did not develop significant hyperglycemia except shortly after STZ treatment. Percentage of insulin-positive B cells in total islet cells and pancreatic immunoreactive insulin (IRI) content were measured at 4 days, 10 days, 4 weeks, and 12 weeks of age. B cells per islet and pancreatic IRI content were significantly reduced in STZ-treated groups as compared with control in both SHR and WKY at 4 days of age, but later they increased significantly with aging in both strains. However, the reduction in pancreatic IRI content relative to control was significantly greater in SHR than in WKY from 4 days (-94.5 +/- 3.5%, -84.1 +/- 4.8%; p < 0.01) to 12 weeks (-97.1 +/- 2.1%, -28.0 +/- 2.5%; p < 0.05), and the reduction in B cells per islet was also greater in SHR at 4 weeks of age. These results indicated that the initial destruction of pancreatic B cells induced by STZ was greater, and the following regeneration was less in SHR than in WKY. The association of the susceptibility to neonatal STZ diabetes with the development of genetic hypertension in SHR remained to be elucidated.

Animals↗
PubMed1994

Angiotensin II alters aortic fibronectin independently of hypertension.

We performed these studies to assess the potential role of hemodynamic forces in mediating the changes in aortic fibronectin mRNA expression that occur in the rat in response to angiotensin II administration. With the use of an acute hypertensive model involving a 3-day infusion with a pressor dose of angiotensin II given by osmotic minipump, a selective increase in fibronectin mRNA expression but not of several other extracellular matrix genes was documented. This change was inhibited by losartan, indicating the importance of angiotensin receptors in the response. Prazosin, hydralazine, or L-arginine added to the drinking water all lowered the angiotensin II-induced increase in blood pressure but did not attenuate the increase in fibronectin mRNA expression. Angiotensin-converting enzyme inhibition using trandolapril did reduce fibronectin mRNA in the angiotensin II-infusion model, despite an inability to reduce blood pressure, whereas when angiotensin I was infused, quinapril lowered both blood pressure and fibronectin expression even at doses that did not completely normalize blood pressure. These studies suggest that angiotensin II induced an increase in aortic fibronectin mRNA that was not dependent solely on blood pressure.

Angiotensin II↗