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H Toh

Publications and source records attributed to H Toh.

At least 109 records · Page 6Linked to original sources
PubMed1987

Role of Mg2+ in the ribozyme system.

Recently, several kinds of catalytic activities have been identified from L-19 IVS RNA or 'ribozyme'. In the catalytic process of ribozyme, Mg2+ is required. We investigated the role of Mg2+ by molecular orbital calculation. Based on the results of the calculation, a model for the self-splicing reaction was constructed.

Animals↗
PubMed1986

T7 and E. coli share homology for replication-related gene products.

Recently, the complete nucleotide sequence of the bacteriophage T7 genome was determined and 50 genes were identified on the genome. We compared amino acid sequences of all the gene products of T7 and replication-related gene products of E. coli. As a result, we found that T7 and E. coli share homology for each pair of exonuclease, DNA primase and helix-destabilizing protein. For E. coli, these gene products are known to be involved in the process of discontinuous DNA replication. These observations suggest that T7 and E. coli have a common origin for a part of their replication systems.

Amino Acid Sequence↗
PubMed1985

Close structural resemblance between putative polymerase of a Drosophila transposable genetic element 17.6 and pol gene product of Moloney murine leukaemia virus.

We have made a computer-assisted search for homology among polymerases or putative polymerases of various viruses and a transposable element, the Drosophila copia-like element 17.6. The search revealed that the putative polymerase (second open reading frame) of the copia-like element 17.6 bears close resemblance in overall structural organization to the pol gene product of Moloney murine leukaemia virus (M-MuLV): they show significant homology to each other at both the N- and C-terminal portions, suggesting that the 17.6 putative polymerase carries two enzymatic activities, related to reverse transcriptase and DNA endonuclease. The putative polymerase of cauliflower mosaic virus (CaMV) shows striking homology with the putative polymerase of 17.6 over almost its entire length, but it lacks the DNA endonuclease-related sequence. Furthermore, it was shown that the N-terminal ends of the M-MuLV pol product and the CaMV and 17.6 putative polymerases exhibit strong sequence homology with the gag-specific protease (p15) of Rous sarcoma virus (RSV) as well as the amino acid sequence predicted from the gag/pol spacer sequence of human adult T-cell leukaemia virus (HTLV). These p15-related sequences contain a highly conserved stretch of amino acids which show a close similarity with sequences around the active site amino acids Asp-Thr-Gly of the acid protease family, suggesting that they have an activity similar to acid protease. On the basis of the alignment of reverse transcriptase-related sequences, a dendrogram representing phylogenetic relationships among all the viruses compared together with 17.6 was constructed and its evolutionary implication is discussed.

Amino Acid Sequence↗
PubMed1985

Evolution of influenza virus genes.

The nucleotide sequences of the eight different influenza A virus segments (genes) were compared among 14 different subtypes. These comparisons demonstrate the presence of molecular clocks in the viral genes; they accumulated both silent and amino acid-changing substitutions at approximately constant rates with respect to time during evolution. In addition, comparison of the rates of evolution among the eight viral genes, excluding the P2 gene, revealed a rapid and roughly equal rate of silent substitution for different genes. The P2 gene exception is explained as the result of recombination (reassortment) between distantly related strains. The rate of amino acid-changing substitution differs greatly from gene to gene. The rate of silent substitution was estimated to be 1.1 X 10(-2)/site/year on the average--that is, about 2 X 10(6) times higher than eukaryotic gene equivalents, which is remarkable. Strain A/USSR/90/77 was shown to evolve with a rate that is similar to those of other strains but to behave as if replication was frozen during a certain period (Nakajima et al. 1978). The frozen period was estimated to be 25 yr on the basis of the molecular clock. A similar analysis revealed another example of frozen replication--in this case, apparently for a period of about 9 yr--in a duck strain, A/duck/Ontario/77.

Amino Acid Sequence↗
PubMed1985

Nucleotide sequence of the Syrian hamster intracisternal A-particle gene: close evolutionary relationship of type A particle gene to types B and D oncovirus genes.

We determined the complete nucleotide sequence of the intracisternal A-particle gene, IAP-H18, cloned from the normal Syrian hamster liver DNA. IAP-H18 was 7,951 base pairs in length with two identical long terminal repeats of 376 base pairs at both ends. On the coding strand, imperfect open reading frames corresponding to gag and pol of the retrovirus genome were observed, whereas many stop codons were present in the region corresponding to env. The putative H18 gag gene (809 amino acids) had a sequence homologous to the N-terminal half of the mouse mammary tumor virus gag gene and locally to the Rous sarcoma virus gag gene. The putative H18 pol gene (900 residues) was homologous to the Rous sarcoma virus pol gene almost throughout the entire region. Two conserved regions among the retrovirus pol genes have been reported. One presumably corresponds to the DNA polymerase and the RNase H domain, and the other corresponds to the DNA endonuclease domain of the multifunctional protein pol. By the comparison of the deduced amino acid sequences of the putative endonuclease domain of six representative oncovirus genomes, a phylogenetic tree of the oncovirus genomes was constructed, and the intracisternal A-particle (type A) genome was found to be more closely related to the mouse mammary tumor virus (type B) and squirrel monkey retrovirus (type D) genomes.

Amino Acid Sequence↗
PubMed1984

Study on the jaw-closing muscle, Adductor mandibulae, of the salmon, Oncorhynchus masou. 1. Fiber types.

A histochemical study has been made on the jaw-closing muscle, Adductor mandibulae, of the Japanese salmon, Oncorhynchus masou. 3 main types of fibers can be distinguished on the basis of differences in SDH activity: 1. fibers with very high SDH activity; 2. fibers with intermediate SDH activity, and 3. fibers with low SDH activity, containing only a few formazan particles. And, fibers with large ranges in diameter were clearly observed in each of the three fiber types classified on the basis of SDH activity. Fibers with the highest SDH activity were recognized in the most medial part of the deep portion, whereas fibers with intermediate activity were mainly distributed in the lateral side of the deep portion. But, there was no discrete zone in the distribution of these fiber types, differing from the locomotor myotomes in the fish. These facts suggest that the A. mandibulae muscle is composed of, at least, more than 3 types of fibers and the function of this muscle is also complex in the fish as it is in the mammalian.

Animals↗
PubMed1983

First observation of a muscle spindle in fish.

In many groups of vertebrates, the muscle spindle is a specialized sensory organ for the detection of muscle stretching. The structure of the spindle varies among vertebrate classes. Moreover, Barker has asserted that Amphibia are the most primitive vertebrates to possess muscle spindles. Extensive studies, made mainly on the locomotor myotome, seem to show that the muscle receptors of fish are less specialized than those of more advanced animals, and that muscle spindles are absent. However, little attention has been paid to the jaw-closing muscle. We report here our finding of a very simple muscle spindle with a single intrafusal fibre in the well-developed jaw-closing muscle, adductor mandibulae, in a primitive teleostean, Oncorhynchus masou (Brevoort).

Animals↗
PubMed1983

Fine structure of the horny teeth of the lamprey, Entosphenus japonicus.

The fine structure of the horny teeth of the lamprey, Entosphenus japonicus, was examined by light- and electron-microscopy. Most of the horny teeth consisted of two horny and two nonhorny layers. The primary horny layer was well keratinized, and the cells were closely packed and intensely interdigitated, being joined together by many modified desmosomes. The plasma membrane of the horny cell, unlike the membranes of other vertebrates, was not thickened. The intercellular spaces were filled with electron-dense material. Microridges were seen on the free surface. Structures resembling microridges were found on the underside of the primary horny layer. The secondary horny layer displayed various stages of keratinization. The keratinization started at the apex and developed toward the base. In the early stage of keratinization, the superficial cells became cylindrical and were arranged in a row forming a dome-shaped line. Their nuclei were situated in the basal part of the cells. The appearance of the nonhorny layers varied according to the degree of keratinization of the horny layers beneath them. The nonhorny cells were joined together by many desmosomes and possessed many tonofilament bundles. The replacement and keratinization of the horny teeth are discussed in the light of these results.

Animals↗
PubMed1981

Studies on the preventive method of lowered ventricular fibrillation threshold during experimental acute myocardial infarctions. A comparison between disopyramide phosphate and lidocaine.

This study was performed to investigate the prophylactic effect of disopyramide phosphate on ventricular fibrillation in acute myocardial infarction. Lidocaine and disopyramide phosphate were compared in terms of their effects on the lowered ventricular fibrillation threshold in experimental myocardial infarction produced by coronary ligation in dogs. The following results were obtained: 1) The effect of lidocaine i.v. + infusion appeared promptly and the ventricular fibrillation threshold exceeded control levels from 45 min onwards (p less than 0.01). 2) The i.m. injection of lidocaine was effective in a dose of 10 mg/Kg. The minimally effective blood level was 1.7 mcg/ml. 3) Disopyramide phosphate 5 mg/Kg i.v. produced a tendency towards recovery from 15 min onwards. After 30 min, the ventricular fibrillation threshold was significantly higher than control (p less than 0.01). 4) Disopyramide phosphate 5 mg/Kg i.m. was initially effective after 45 min. The effect was significant from 1 hour and 30 min onwards, compared with control (p less than 0.01). The minimally effective blood level was 2.4 mcg/ml. 5) Disopyramide phosphate 2 mg/Kg i.m. produced a tendency towards recovery but the difference from the control was not significant. 6) In equivalent i.m. doses, disopyramide phosphate tended to be more potent than lidocaine in increasing the ventricular fibrillation threshold. 7) In the aforementioned doses, disopyramide phosphate did not cause any marked changes in PQ interval or QT time in ECG. These results suggest that the intramuscular injection of disopyramide phosphate is a hopeful clinical treatment to prevent ventricular fibrillation in the very early stages of acute myocardial infarction.

Animals↗
PubMedDate not supplied

Sequence homology between retroviral reverse transcriptase and putative polymerases of hepatitis B virus and cauliflower mosaic virus.

In infected cells, the RNA genomes of RNA tumour viruses are copied into DNA by a virus-encoded reverse transcriptase enzyme. This transfer of information from RNA into DNA was thought to be a unique feature of RNA tumour viruses, but recent results suggest it may be a more general strategy. Hepatitis B virus (HBV) has a double-stranded DNA genome, and it has recently been shown that the minus DNA strand of the HBV genome is copied from a plus-strand RNA template, leading to the suggestion that reverse transcription is central to the life cycle of HBV. More recently it has been suggested that the replication cycle of a plant virus, cauliflower mosaic virus (CaMV), includes a reverse transcription step. We report here the existence of amino acid sequence homology between retroviral reverse transcriptase and the putative polymerases of HBV and CaMV.

Amino Acid Sequence↗