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S Osawa

Publications and source records attributed to S Osawa.

At least 109 records · Page 6Linked to original sources
PubMed1990

The organization and evolution of transfer RNA genes in Mycoplasma capricolum.

The genes for presumably all the tRNA species in Mycoplasma capricolum, a derivative of Gram-positive eubacteria, have been cloned and sequenced. There are 30 genes encoding 29 tRNA species. This number is the smallest in all the known genetic systems except for mitochondria. The sequences of 9 tRNA genes of them have been previously reported (1-3). Twenty-two genes are organized in 5 clusters consisting of nine, five, four and two genes (2 sets), respectively. The other eight genes exist as a single transcription unit. All the tRNAs are encoded each by a single gene, except for the occurrence of two tRNA(Lys)(TTT) genes. The arrangement of tRNA genes in the 9-gene cluster, the 5-gene cluster, the 4-gene cluster and one of the 2-gene clusters reveals extensive similarity with a part of the 21-tRNA gene cluster and/or the 16-tRNA gene cluster in Bacillus subtilis, respectively. The results suggest that the present M. capricolum tRNA genes have evolved from large tRNA gene clusters in the ancestral Gram-positive bacterial genome common to M. capricolum and B. subtilis, by discarding genes for redundant as well as non-obligate tRNAs, so that all the codons may be translated by as small a number of tRNAs as possible.

Base Sequence↗
PubMed1990

A G protein mutant that inhibits thrombin and purinergic receptor activation of phospholipase A2.

The stimulation of phospholipase A2 by thrombin and type 2 (P2)-purinergic receptor agonists in Chinese hamster ovary cells is mediated by the G protein Gi. To delineate alpha chain regulatory regions responsible for control of phospholipase A2, chimeric cDNAs were constructed in which different lengths of the alpha subunit of Gs (alpha s) were replaced with the corresponding sequence of the Gi alpha subunit (alpha i2). When a carboxyl-terminal chimera alpha s-i(38), which has the last 38 amino acids of alpha s substituted with the last 36 residues of alpha i2, was expressed in Chinese hamster ovary cells, the receptor-stimulated phospholipase A2 activity was inhibited, although the chimera could still activate adenylyl cyclase. Thus, alpha s-i(38) is an active alpha s, but also a dominant negative alpha i molecule, indicating that the last 36 amino acids of alpha i2 are a critical domain for G protein regulation of phospholipase A2 activity.

Adenosine Triphosphate↗
PubMed1990

Evolutionary changes in the genetic code.

The genetic code has been influenced by directional mutation pressure affecting the base composition of DNA, sometimes in the direction of increased GC content and at other times, in the direction of AT. Such pressure led to changes in species-specific usages of codons and tRNA anticodons, and also in amino acid assignments of codons in mitochondria and in several intact organisms. These code changes are probably recent evolutionary events. The genetic code is not 'frozen', but instead it is still evolving.

Base Sequence↗
PubMed1990

Role of GC-biased mutation pressure on synonymous codon choice in Micrococcus luteus, a bacterium with a high genomic GC-content.

The GC (G + C, or G or C)-contents of codon silent positions in all two-codon sets and three codons AUY/A (IIe), and in most of the family boxes of Micrococcus luteus (genomic GC-content: 74%) are 95% to 100% in both the highly and weakly expressed genes. In some family boxes, there is a decrease in NNC codons and an increase in NNG codons from the highly expressed to weakly expressed genes without apparent involvement of NNU and NNA codons. From these observations, we conclude that the selective use of synonymous codons in M. luteus may be largely determined by GC-biased mutation pressure and that in the highly expressed genes tRNAs would act as a weak selection pressure in some family boxes. Available data suggest that the effect of selection pressure by tRNAs on the synonymous codon choice becomes more apparent in the highly expressed genes in eubacteria with intermediate GC-contents such as Escherichia coli and Bacillus subtilis, and that the U/C ratio of the codon third positions in NNU/C-type two-codon sets in the weakly expressed genes would represent the approximate magnitude of directional mutation pressure throughout eubacteria.

Base Sequence↗
PubMed1990

Evolution of the mitochondrial genetic code. III. Reassignment of CUN codons from leucine to threonine during evolution of yeast mitochondria.

Yeast mitochondria use UUR as the sole leucine codons. CUN, universal leucine codons, are read as threonine by aberrant threonine tRNA with anticodon sequence (UAG). The reassignment of CUN codons to threonine during yeast mitochondrial evolution could have proceeded by the disappearance of CUN codons from the reading frames of messenger RNA, through mutation mainly to UUR leucine codons as a result of AT pressure. We suggest that this was accompanied by a loss of leucine-accepting ability of tRNA Leu(UAG). This tRNA could have then acquired threonine-accepting activity through the appearance of an additional threonyl-tRNA synthetase. CUN codons that subsequently appeared from mutations of various other codons would have been translated as threonine. This change in the yeast mitochondrial genetic code is likely to have evolved through a series of nondisruptive nucleotide substitutions that produced no widespread replacement of leucine by threonine in proteins as a consequence.

Adenine↗
PubMed1990

Mutation of the Gs protein alpha subunit NH2 terminus relieves an attenuator function, resulting in constitutive adenylyl cyclase stimulation.

G-proteins couple hormonal activation of receptors to the regulation of specific enzymes and ion channels. Gs and Gi are G-proteins which regulate the stimulation and inhibition, respectively, of adenylyl cyclase. We have constructed two chimeric cDNAs in which different lengths of the alpha subunit of Gs (alpha s) have been replaced with the corresponding sequence of the Gi alpha subunit (alpha i2). One chimera, referred to as alpha i(54)/s' replaces the NH2-terminal 61 amino acids of alpha s with the first 54 residues of alpha i. Within this sequence there are 7 residues unique to alpha s, and 16 of the remaining 54 amino acids are nonhomologous between alpha i and alpha s. The second chimera, referred to as alpha i/s(Bam), replaces the first 234 amino acids of alpha s with the corresponding 212 residues of alpha i. Transient expression of alpha i(54)/s in COS-1 cells resulted in an 18- to 20-fold increase in cyclic AMP (cAMP) levels, whereas expression of either alpha i/s(Bam) or the wild-type alpha s polypeptide resulted in only a 5- to 6-fold increase in cellular cAMP levels. COS-1 cells transfected with alpha i showed a small decrease in cAMP levels. Stable expression of the chimeric alpha i(54)/s polypeptide in Chinese hamster ovary (CHO) cells constitutively increased both cAMP synthesis and cAMP-dependent protein kinase activity. CHO clones expressing transfected alpha i/s(Bam) or the wild-type alpha s and alpha i cDNAs exhibited cAMP levels and cAMP-dependent protein kinase activities similar to those in control CHO cells. Therefore, the alpha i(54)/s chimera behaves as a constitutively active alpha s polypeptide, whereas the alpha i/s(Bam) polypeptide is regulated similarly to wild-type alpha s. Expression in cyc-S49 cells, which lack expression of wild-type alpha s, confirmed that the alpha i(54)/s polypeptide is a highly active alpha s molecule whose robust activity is independent of any change in intrinsic GTPase activity. The difference in phenotypes observed upon expression of alpha i(54)/s or alpha i/s(Bam) indicates that the NH2-terminal moieties of alpha s and alpha i function as attenuators of the effector enzyme activator domain which is within the COOH-terminal half of the alpha subunit. Mutation at the NH2 terminus of alpha s relieves the attenuator control of the Gs protein and results in a dominant active G-protein mutant.

1-Methyl-3-isobutylxanthine↗
PubMed1990

[Study for improvement of oral health among the elderly. Present status of dental care service at elderly homes].

Since the dental environment at a living place could potentially become a factor causing a need for dental care, all 33 elderly homes (27 of which responded to the survey) in Tokyo were investigated for the purpose of identifying the present status of dental care service and the problems existing at these homes. The following are the obtained conclusions. 1. The rate of homes with dental care facilities is as low as 19.2%, and cooperation by dental care institutions, including house calls, is ensured only at the low rate of 11.1%. As a result, usually patients visit the dental institutions. 2. The involvement of the dental staff, including part-time, was 44.4%, less than half of the homes surveyed. The homes wishing to employ or receive service from dental staff accounted for 76.9%. The homes also expected them to be engaged in the activities of overall oral hygiene, including not only dental treatment, but also participation in the planning of oral hygienic management. However, 23.1% of the respondents did not wish to employ any dental staff or receive any such service. 3. Specific programs for the guidance and management of oral hygiene were not observed. Homes that conducted dental examination periodically and those that carried out activities related to oral hygiene during Dental Health Week were also lacking. In addition, the homes which had assigned personnel responsibility for oral hygiene represented only 12.0%.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Codon recognition patterns as deduced from sequences of the complete set of transfer RNA species in Mycoplasma capricolum. Resemblance to mitochondria.

The nucleotide sequences of the complete set of tRNA species in Mycoplasma capricolum, a derivative of Gram-positive eubacteria, have been determined. This bacterium represents the first genetic system in which the sequences of all the tRNA species have been determined at the RNA level. There are 29 tRNA species: three for Leu, two each for Arg, Ile, Lys, Met, Ser, Thr and Trp, and one each for the other 12 amino acids as judged from aminoacylation and the anticodon nucleotide sequences. The number of tRNA species is the smallest among all known genetic systems except for mitochondria. The tRNA anticodon sequences have revealed several features characteristic of M. capricolum. (1) There is only one tRNA species each for Ala, Gly, Leu, Pro, Ser and Val family boxes (4-codon boxes), and these tRNAs all have an unmodified U residue at the first position of the anticodon. (2) There are two tRNAThr species having anticodons UGU and AGU; the first positions of these anticodons are unmodified. (3) There is only one tRNA with anticodon ICG in the Arg family box (CGN); this tRNA can translate codons CGU, CGC and CGA. No tRNA capable of translating codon CGG has been detected, suggesting that CGG is an unassigned codon in this bacterium. (4) A tRNATrp with anticodon UCA is present, and reads codon UGA as Trp. On the basis of these and other observations, novel codon recognition patterns in M. capricolum are proposed. A comparatively small total, 13, of modified nucleosides is contained in all M. capricolum tRNAs. The 5' end nucleoside of the T psi C-loop (position 54) of all tRNAs is uridine, not modified to ribothymidine. The anticodon composition, and hence codon recognition patterns, of M. capricolum tRNAs resemble those of mitochondrial tRNAs.

Amino Acids↗
PubMed1989

Mutation of glycine 49 to valine in the alpha subunit of GS results in the constitutive elevation of cyclic AMP synthesis.

The G-protein GS couples hormone-activated receptors with adenylyl cyclase and stimulates increased cyclic AMP synthesis. Transient expression in COS-1 cells of cDNAs coding for the GS alpha-subunit (alpha S) or alpha S cDNAs having single amino acid mutations Gly49----Val or Gly225----Thr elevated cyclic AMP levels, resulting in the activation of cyclic AMP dependent protein kinase. Stable expression in Chinese hamster ovary cells of alpha S Val49 cDNA resulted in a small constitutive elevation of cyclic AMP that was sufficient to persistently activate cyclic AMP dependent protein kinase activity 1.5-2-fold over basal activity. Stable expression of wild-type alpha S or alpha S Thr225 in Chinese hamster ovary cells was less effective in sustaining elevated cyclic AMP synthesis and kinase activation compared to alpha SVal49.

Animals↗
PubMed1989

Micrococcus luteus, a bacterium with a high genomic G + C content, contains Escherichia coli-type promoters.

The G + C content of Micrococcus luteus DNA is 74%, which is much higher than that of Escherichia coli (about 50%). In order to understand the influence of GC-directed mutation pressure (GC pressure) on the promoter structure, the initiation sites for both in vitro and in vivo transcription of M. luteus streptomycin (str) and spectinomycin (spc) operons were identified by the reverse transcriptase mapping method. The promoter sequences of M. luteus are similar to those of E. coli, but have significantly higher G + C contents. In an in vitro run-off transcription assay using truncated DNA templates, RNA polymerases from both M. luteus and E. coli were able to transcribe correctly from both the str promoter and the spc major promoter of M. luteus.

Base Sequence↗
PubMed1989

Evolution of the mitochondrial genetic code. I. Origin of AGR serine and stop codons in metazoan mitochondria.

AGA and AGG (AGR) are arginine codons in the universal genetic code. These codons are read as serine or are used as stop codons in metazoan mitochondria. The arginine residues coded by AGR in yeast or Trypanosoma are coded by arginine CGN throughout metazoan mitochondria. AGR serine sites in metazoan mitochondria are occupied mainly in corresponding sites in yeast or Trypanosoma mitochondria by UCN serine, AGY serine, or codons for amino acids other than serine or arginine. Based on these observations, we propose the following evolutionary events. AGR codons became unassigned because of deletion of tRNA Arg (UCU) and elimination of AGR codons by conversion to CGN arginine codons. Upon acquisition by serine tRNA of pairing ability with AGR codons, some codons for amino acids other than arginine mutated to AGR, and were captured by anticodon GCU in serine tRNA. During vertebrate mitochondrial evolution, AGR stop codons presumably were created from UAG stop by deletion of the first nucleotide U and by use of R as the third nucleotide that had existed next to the ancestral UAG stop.

Animals↗
PubMed1989

Codon reassignment (codon capture) in evolution.

The genetic code, once thought to be "frozen," shows variations from the universal code. Variations are found in mitochondria, Mycoplasma, and ciliated protozoa. The variations result from reassignment of codons, especially stop codons. The reassignments take place by disappearance of a codon from coding sequences, followed by its reappearance in a new role. Simultaneously, a changed anticodon must appear. We discuss the role of directional mutation pressure in the events, and we also describe the possibility that such events have taken place during early evolution of the genetic code and can occur during its present evolution.

Animals↗
PubMed1989

Evolution of the mitochondrial genetic code. II. Reassignment of codon AUA from isoleucine to methionine.

The reassignment of codon AUA from isoleucine to methionine during mitochondrial evolution may be explained by the codon reassignment (capture) hypothesis without assuming direct replacement of isoleucine by methionine in mitochondrial proteins. According to this hypothesis, codon AUA would have disappeared from the reading frames of messenger RNA. AUA codons would have mutated mainly to AUU isoleucine codons because of constraints resulting from elimination of tRNA Ile with anticodon *CAU (in which *C is lysidine). Later, tRNA Met (CAU) would have undergone structural changes enabling it to pair with both AUG and AUA. AUA codons, formed by mutations of other codons, including AUG, would have reappeared and would have been translated as methionine.

Animals↗
PubMed1989

Spectinomycin operon of Micrococcus luteus: evolutionary implications of organization and novel codon usage.

The complete DNA sequence of the Micrococcus luteus spectinomycin (spc) operon and its adjacent regions has been determined. The sequence has revealed the presence of genes that are homologous to those of the Escherichia coli ribosomal and related proteins, L14, L24, L5, S8, L6, L18, S5, L30, L15, and secretion protein Y (sec Y), and the gene for adenylate kinase (adk). The gene arrangement in the spc operon is essentially the same as that of E. coli except for the absence in the M. luteus spc operon of the genes for S14 and X protein that exist in the E. coli spc operon. SecY and adk seem to be composed of another operon (adk operon) with at least an open reading frame. The deduced amino acid sequences for these ribosomal proteins are well conserved among the two species (40-65% identity). Reflecting the high genomic guanine and cytosine (GC) content of M. luteus (74%), the codon usage of the genes is extremely biased toward use of G and C, about 94% of the codon third positions being G or C. Seven codons, AUA, AAA, AGA, UUA, GUA, CUA, and CAA, all of which have A at the codon third positions, are completely absent in the M. luteus genes examined. Out of 11 genes in the M. luteus spc and adk operons, 5 (10) use GUG (UGA) and 6 (1) use AUG (UAA) as an initiation (termination) codon.

Amino Acid Sequence↗
PubMed1989

Evolutionary relationship of archaebacteria, eubacteria, and eukaryotes inferred from phylogenetic trees of duplicated genes.

All extant organisms are though to be classified into three primary kingdoms, eubacteria, eukaryotes, and archaebacteria. The molecular evolutionary studies on the origin and evolution of archaebacteria to date have been carried out by inferring a molecular phylogenetic tree of the primary kingdoms based on comparison of a single molecule from a variety of extant species. From such comparison, it was not possible to derive the exact evolutionary relationship among the primary kingdoms, because the root of the tree could not be determined uniquely. To overcome this difficulty, we compared a pair of duplicated genes, elongation factors Tu and G, and the alpha and beta subunits of ATPase, which are thought to have diverged by gene duplication before divergence of the primary kingdoms. Using each protein pair, we inferred a composite phylogenetic tree with two clusters corresponding to different proteins, from which the evolutionary relationship of the primary kingdoms is determined uniquely. The inferred composite trees reveal that archaebacteria are more closely related to eukaryotes than to eubacteria for all the cases. By bootstrap resamplings, this relationship is reproduced with probabilities of 0.96, 0.79, 1.0, and 1.0 for elongation factors Tu and G and for ATPase subunits alpha and beta, respectively. There are also several lines of evidence for the close sequence similarity between archaebacteria and eukaryotes. Thus we propose that this tree topology represents the general evolutionary relationship among the three primary kingdoms.

Adenosine Triphosphatases↗