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Biomedical subjects

I Miyajima

Publications and source records attributed to I Miyajima.

30 records · Page 2Linked to original sources
PubMed1988

Isolation of a second yeast Saccharomyces cerevisiae gene (GPA2) coding for guanine nucleotide-binding regulatory protein: studies on its structure and possible functions.

In a previous paper, we demonstrated that a gene coding for a protein homologous to the alpha subunit of mammalian guanine nucleotide-binding regulatory (G) proteins occurs in Saccharomyces cerevisiae. The gene, designated GPA1, encodes a protein (GP1 alpha) of 472 amino acids with a calculated Mr of 54,075. Here we report the isolation of another G-protein-homologous gene, GPA2, which encodes an amino acid sequence of 449 amino acid residues with a Mr of 50,516. The predicted primary structure of the GPA2-encoded protein (GP2 alpha) is homologous to mammalian G proteins [inhibitory and stimulatory G proteins (Gi and Gs, respectively), a G protein of unknown function (Go), and transducins (Gt)] as well as yeast GP1 alpha. When aligned with the alpha subunit of Gi (Gi alpha) to obtain maximal homology, GP2 alpha was found to contain a stretch of 83 additional amino acid residues near the NH2 terminus. The gene was mapped in chromosome V, close to the centromere. Haploid cells carrying a disrupted GPA2 gene are viable. Cells carrying a high copy number of plasmid GPA2 (YEpGPA2) had markedly elevated levels of cAMP and could suppress a temperature-sensitive mutation of RAS2. These results suggest that GPA2 may be involved in the regulation of cAMP levels in S. cerevisiae.

Amino Acid Sequence↗
PubMed1988

Suppressors of a gpa1 mutation cause sterility in Saccharomyces cerevisiae.

The Saccharomyces cerevisiae GPA1 gene encodes a protein highly homologous to the alpha subunit of mammalian G proteins and is essential for haploid cell growth. We have selected 77 mutants able to suppress the lethality resulting from disruption of GPA1 (gpa1::HIS3). Two strains bearing either of two recessive mutations, sgp1 and sgp2, in combination with the disruption mutation, showed a cell type nonspecific sterile phenotype, yet expressed the major alpha-factor gene (MF alpha 1) as judged by the ability to express a MF alpha 1-lacZ fusion gene. The sgp1 mutation was closely linked to gpa1::HIS3 and probably occurred at the GPA1 locus. The sgp2 mutation was not linked to GPA1 and was different from the previously identified cell type nonspecific sterile mutations (ste4, ste5, ste7, ste11 and ste12). sgp2 GPA1 cells showed a fertile phenotype, indicating that the mating defect caused by sgp2 is associated with the loss of GPA1 function. While expression of a FUS1-lacZ fusion gene was induced in wild-type cells by the addition of alpha-factor, mutants bearing sgp1 or sgp2 as well as gpa1::HIS3 constitutively expressed FUS1-lacZ. These observations suggest that GPA1 (SGP1) and SGP2 are involved in mating factor-mediated signal transduction, which causes both cell cycle arrest in the late G1 phase and induction of genes necessary for mating such as FUS1.

Cell Cycle↗
PubMed1987

GPA1, a haploid-specific essential gene, encodes a yeast homolog of mammalian G protein which may be involved in mating factor signal transduction.

GPA1 protein of Saccharomyces cerevisiae is homologous to the alpha subunit of mammalian G protein. GPA1 transcript was found in haploid cells but was not detected in diploid cells. Disruption of GPA1 resulted in a haploid-specific lethal phenotype, indicating that GPA1 is a haploid-specific essential gene for cell growth. Upon regulation of expression of GPA1 by the galactose-inducible GAL1 promoter, the loss of GPA1 function was found to lead to cell-cycle arrest at the late G1 phase. Mutants that suppress the lethality of the gpa1::HIS3 mutation showed a sterile phenotype that was not cell-type-specific. These results suggest that GPA1 protein may control the signal for mating-factor-mediated cell-cycle arrest.

Cell Cycle↗
PubMed1985

The clinical significance of the tympanic isthmus related to the development of cholesteatoma.

The epitympanum is separated from the mesotympanum by the ossicles, tendons and tympanic mucosal folds except at two narrow openings, the anterior and posterior tympanic isthmuses. Using large numbers of fresh cadaver temporal bone specimens, anatomical boundaries of the tympanic isthmus were defined and pathological variations were investigated in relation to the development of aural cholesteatoma. A total of 170 temporal bone specimens were examined under the operating microscope. Five of these were found to have middle ear diseases, most of which were cholesteatoma or a preliminary state of cholesteatoma, with their tympanic isthmuses obstructed or narrowed. Pneumatization of the mastoid was inhibited in all of the pathological specimens. From the results of temporal bone dissection supplemented by analysis of surgical findings in cholesteatoma, we have divided acquired cholesteatoma into two types: the pars flaccida-type cholesteatoma (attic retraction-type) and the pars tensa type. The close relationship between the development of cholesteatoma and occlusion of the tympanic isthmus is examined herein.

Adult↗
PubMed1984

Analysis of full-length cDNA clones carrying GAL1 of Saccharomyces cerevisiae: a model system for cDNA expression.

A cDNA cloning vector that allows expression in Saccharomyces cerevisiae has been developed using the plasmid primer approach described by Okayama and Berg [Mol. Cell. Biol. 2:161-170(1982)]. The vector contains ARS1 and TRP1 for plasmid maintenance in yeast and the ADC1 or GAL1 promoter and the TRP5 terminator for expression of the cloned cDNA. Using this system, several recombinants with nearly full-length GAL1 cDNA inserts in a cDNA library made with galactose-induced yeast mRNA were identified. By measurement of galactokinase mRNA and its protein, the expression of GAL1 cDNA was shown to be under the control of the promoter placed upstream of the cDNA insert. Nucleotide sequence analysis revealed that the 3'-ends of the GAL1 cDNA inserts were not unique, indicating that polyA tails were added to GAL1 transcripts at multiple sites in the GAL1 gene. Genetic complementation of appropriate yeast mutants permitted the isolation of clones containing the coding sequences for GAL1, HIS3, and LEU2 from the same cDNA library.

Base Sequence↗
PubMed1984

Expression of plasmid R388-encoded type II dihydrofolate reductase as a dominant selective marker in Saccharomyces cerevisiae.

The R388 plasmid-encoded drug-resistant type II dihydrofolate reductase gene (R . dhfr) was expressed in Saccharomyces cerevisiae by fusing the R . dhfr coding sequence to the yeast TRP5 promoter. Yeast cells harboring these recombinant plasmids grew in media with 10 micrograms of methotrexate per ml and 5 mg of sulfanilamide per ml, a condition which inhibits the growth of wild-type cells. Addition of a 390-base-pair fragment from the 3'-noncoding region of TRP5 downstream from R . dhfr increased expression. Presumably, the added segment promoted termination or polyadenylation or both of the R . dhfr transcript. The activity of the plasmid-encoded dihydrofolate reductase and the copy number of the R . dhfr plasmid in cells grown in drug-selective media were higher by one order of magnitude than those grown in nutrition-selective media. Plasmid copy number, as well as the plasmid-encoded enzyme level, decreased when cells were selected for prototrophy. In drug-selective media, the plasmid-encoded enzyme level and the content of R . dhfr transcripts were nearly constant in cells harboring R . dhfr plasmids containing different yeast promoters. In contrast, the plasmid copy number and beta-lactamase activity encoded in cis by plasmids were much higher when R . dhfr was associated with the weak TRP5 promoter than when it was fused to the strong ADC1 promoter. These results indicate that plasmid copy number, i.e., gene dosage of R . dhfr, correlates inversely with the strength of the promoter associated with R . dhfr, and cells with a higher plasmid copy number were enriched in drug-selective media. The transformation efficiency of R . dhfr fused to the ADC1 promoter was almost the same on drug-selective plates as on nutrition-selective plates, indicating that R . dhfr is suitable as a dominant selective transformation marker in S. cerevisiae.

DNA Restriction Enzymes↗
PubMedDate not supplied

The incidence of hepatocellular carcinoma in patients with chronic hepatitis C after interferon treatment.

To determine whether serum hepatitis C virus (HCV) RNA disappearance after interferon (IFN) treatment prevents development of hepatocellular carcinoma (HCC), we evaluated retrospectively the incidence of HCC in patients with chronic hepatitis C. A total of 213 patients were monitored for more than 6 months after completion of IFN treatment. Sixty-three of the 213 patients (29.6%) achieved a complete response (CR) to treatment and 150 (70.4%) had no response (NR). HCC developed in 12 (5.6%), all of whom were NR. Logistic analysis showed age, alpha -fetoprotein, and staging of histological finding before IFN treatment were independent factors to development of HCC. The fact that there was no HCC development from CR provides a basis for IFN treatment in chronic HCV infection.

Adult↗