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Biomedical subjects

M Yanagida

Publications and source records attributed to M Yanagida.

At least 199 records · Page 11Linked to original sources
PubMed1989

Higher order chromosome structure is affected by cold-sensitive mutations in a Schizosaccharomyces pombe gene crm1+ which encodes a 115-kD protein preferentially localized in the nucleus and its periphery.

We isolated a novel class of Schizosaccharomyces pombe cold-sensitive mutants with deformed nuclear chromosome domains consisting of thread- or rodlike condensed segments at restrictive temperature. Their mutations were mapped in a novel, identical locus designated crm1 (chromosomal region maintenance). The crm1 mutants also show the following phenotypes. DNA, RNA, and protein syntheses diminish at restrictive temperature. At permissive temperature, the amount of one particular protein, p25, greatly increases. The mutant growth is hypersensitive to Ca2+ and resistant to protein kinase inhibitors. We cloned the 4.1-kb-long crm1+ gene that rescued the above phenotypes by transformation and determined its nucleotide sequence, which predicts a 1,077-residue protein. Affinity-purified antiserum raised against the crm1+ polypeptide expressed in Escherichia coli detected a 115-kD protein in S. pombe extracts. Genomic Southern hybridization and immunoblotting suggested that the crm1+ product might be highly conserved in distant organisms. Through immunofluorescence microscopy, the crm1+ protein appeared to be principally localized within the nucleus and also at its periphery. We speculate that the crm1+ protein might be one of those nuclear components that modify the chromosome structures or regulate the nuclear environment required for maintaining higher order chromosome structures.

Amino Acid Sequence↗
PubMed1989

Recurrent bacterial meningitis. Secondary to malformation of the inner ear.

A 5-year-old girl with congenital sensorial deafness experienced four episodes of bacterial meningitis in a 13-month period. On the fourth episode, an extensive search for the cause of recurrent meningitis was conducted. Complete immunologic studies, humoral, cellular, and phagocytic, yielded negative results. Precise otological examination, i.e., skull roentgenograms, an inner ear target CT scan, and puncture of the eardrum, was attempted, which disclosed the inner ear malformation (Mondini's anomaly) and a cerebrospinal fluid (CSF) fistula. CSF discharge from the oval window was repaired surgically. Extensive otologic evaluation should be conducted in patients with recurrent bacterial meningitis.

Cerebrospinal Fluid Otorrhea↗
PubMed1989

Gene products required for chromosome separation.

Gene products required for mitotic chromosome separation in the fission yeast Schizosaccharomyces pombe are described. They have been identified by two distinct strategies of mutant isolation, followed by gene cloning and immunochemical characterization of gene products. The roles of four representative genes, namely nda3+, nuc2+, top2+ and dis2+, encoding beta-tubulin, a nuclear scaffold-like protein, DNA topoisomerase II and type-1 protein phosphatase, respectively, are discussed in regard to the mechanisms and control of chromosome separation.

Chromosomes, Fungal↗
PubMed1988

Cold-sensitive and caffeine-supersensitive mutants of the Schizosaccharomyces pombe dis genes implicated in sister chromatid separation during mitosis.

We isolated novel classes of Schizosaccharomyces pombe cold-sensitive dis mutants that block mitotic chromosome separation (nine mapped in the dis1 gene and one each in the dis2 and dis3 genes). Defective phenotype at restrictive temperature is similar among the mutants; the chromosomes condense and anomalously move to the cell ends in the absence of their disjoining so that they are unequally distributed at the two cell ends. Synchronous culture analyses indicate that the cells can enter into mitosis at normal timing but become lethal during mitosis. In comparison with the wild-type mitosis, defects are found in the early spindle structure, the mitotic chromosome structure, the poleward chromosome movement by the spindle elongation and the telophase spindle degradation. The dis mutants lose at permissive temperature an artificial minichromosome at higher rates than occur in the wild type. We found that all the dis mutants isolated are supersensitive to caffeine at permissive temperature. Furthermore, the mutant cells in the presence of caffeine produce a phenotype similar to that obtained at restrictive temperature. We suggest that the dis genes are required for the sister chromatid separation at the time of mitosis and that caffeine might affect the dis gene expression. We cloned, in addition to the dis2+ and dis3+ genes, multicopy extragenic suppressor sequences which complement dis1 and dis2 mutations. A complex regulatory system may exist for the execution of the dis+ gene functions.

Caffeine↗
PubMed1988

A temperature-sensitive mutation of the Schizosaccharomyces pombe gene nuc2+ that encodes a nuclear scaffold-like protein blocks spindle elongation in mitotic anaphase.

A temperature-sensitive mutant nuc2-663 of the fission yeast Schizosaccharomyces pombe specifically blocks mitotic spindle elongation at restrictive temperature so that nuclei in arrested cells contain a short uniform spindle (approximately 3-micron long), which runs through a metaphase plate-like structure consisting of three condensed chromosomes. In the wild-type or in the mutant cells at permissive temperature, the spindle is fully extended approximately 15-micron long in anaphase. The nuc2' gene was cloned in a 2.4-kb genomic DNA fragment by transformation, and its complete nucleotide sequence was determined. Its coding region predicts a 665-residues internally repeating protein (76.250 mol wt). By immunoblots using anti-sera raised against lacZ-nuc2+ fused proteins, a polypeptide (designated p67; 67,000 mol wt) encoded by nuc2+ is detected in the wild-type S. pombe extracts; the amount of p67 is greatly increased when multi-copy or high-expression plasmids carrying the nuc2+ gene are introduced into the S. pombe cells. Cellular fractionation and Percoll gradient centrifugation combined with immunoblotting show that p67 cofractionates with nuclei and is enriched in resistant structure that is insoluble in 2 M NaCl, 25 mM lithium 3,5'-diiodosalicylate, and 1% Triton but is soluble in 8 M urea. In nuc2 mutant cells, however, soluble p76, perhaps an unprocessed precursor, accumulates in addition to insoluble p67. The role of nuc2+ gene may be to interconnect nuclear and cytoskeletal functions in chromosome separation.

Amino Acid Sequence↗
PubMed1987

Cloning and sequencing of Schizosaccharomyces pombe DNA topoisomerase I gene, and effect of gene disruption.

We cloned the structural gene topl+ for Schizosaccharomyces pombe DNA topoisomerase I (topo I) by hybridization. An eight-fold increase of topo I relaxing activity was obtained in S. pombe cells transformed with multicopy plasmid with topl+ insert. Nucleotide sequence determination showed a hypothetical coding frame interrupted by two short introns, encoding a 812 residue polypeptide (M.W. 94,000), 43 residues longer than and 47% homologous to Saccharomyces cerevisiae topo I. We show that the topl (null) strain made by gene disruption is viable, although its generation time is 20% longer than that of wild type. The topl locus is mapped in the long arm of chromosome II, using the Leu+ marker integrated with the cloned topl+ sequence. We constructed a double mutant topl (null) top2 (ts) and found its defective phenotype similar to that of previously obtained topl (heat sensitive) top2 (ts). The other double mutant topl (null) top2 (cs), however, was lethal. Our results suggest that topl+ gene of S. pombe is dispensable only if topo II activity is abundant.

Amino Acid Sequence↗
PubMed1987

DNA topoisomerase II is required for condensation and separation of mitotic chromosomes in S. pombe.

We show that DNA topoisomerase II (topo II) is continuously required for mitotic chromosome changes in Schizosaccharomyces pombe. We constructed cold-sensitive (cs) or temperature-sensitive (ts) strains mutated in the genes coding for topo II (top2) and beta-tubulin (nda3). The ATP-dependent activity of the top2cs gene product is cs in vitro. The cloned top2cs gene sequence predicts an amino acid substitution. A cs top2-cs nda3 double mutant at 20 degrees C shows long, entangled chromosomes, which condense and separate upon the shift to permissive temperatures. If spindle formation is prevented at permissive temperatures, the chromosomes condense but do not separate. Thus topo II is required for final chromosome condensation; moreover, pulse-shift experiments show that topo II is required for chromatid disjuction. Experiments with ts top2-cs nda3 cells show that topo II is also required for chromosome separation in anaphase: inactivation of topo II and activation of beta-tubulin allow normal spindle formation but result in "streaked" chromosomes.

Adenosine Triphosphate↗
PubMed1987

A novel sequence common to the centromere regions of Schizosaccharomyces pombe chromosomes.

An approximately 4 kb long sequence (designated dh) is located in the centromere regions of all three chromosomes of S. pombe. There is one copy each of dh per centromere in chromosomes I and II and multiples in the centromere of chromosome III. Nucleotide sequence determination shows that dhI and dhII are highly homologous. A part of the sequence (ca. 300-400 bp) contains short direct repeats, otherwise dh is in general internally non-repetitious. Although there are three segmental deletions (total 821 bp) and two insertions (27 bp) in dhII (an 80% overall homology to dhI), there are only nine substitutions between dhI and dhII in the remaining 3980 bp, giving a 99.77% homology. The substitutions are restricted to the non-repetitious domains and are only of the pyrimidine-pyrimidine or purine-purine types. A possible conformational role of dh is discussed.

Base Sequence↗
PubMed1987

Histone transcription in cell cycle mutants of fission yeast.

The level of histone H2B transcripts peak during S-phase of the fission yeast Schizosaccharomyces pombe. The pattern of transcript accumulation has been monitored in temperature-sensitive mutants which block at different times during the cell cycle, at start in G1 where the cell becomes committed to the mitotic cycle, in G1 after start, and during S-phase. Cells blocked before start using cdc10-129 do not accumulate histone H2B transcripts, but cells blocked after start using cdc22-C11 do show accumulation. Transcript levels increase in another mutant cdc20-M10 which also blocks in G1. These experiments establish that histone H2B transcripts increase in level in preparation for S-phase during late G1 before any DNA synthesis. Passage of start begins a sequence of events leading to S-phase which includes an increase in histone H2B transcript levels. In the cdc20 and cdc22 mutants transcript levels do not decrease normally suggesting that the signals which lead to the fall in level are not given in these G1-arrested cells. The mutants cdc17-K42 (defective in DNA ligase) and cdc24-M38 block in late S-phase after the DNA content has doubled. Histone H2B transcripts increase normally but remain at a high level. In these mutants even though DNA content has doubled, the mechanisms which lead to a fall in transcript levels appear not to be brought into play.

Journal Article↗
PubMed1987

Identification of healed terminal DNA fragments in linear minichromosomes of Schizosaccharomyces pombe.

The minichromosome Ch16 of the fission yeast Schizosaccharomyces pombe is derived from the centromeric region of chromosome III. We show that Ch16 and a shorter derivative, Ch12, made by gamma-ray cleavage, are linear molecules of 530 and 280 kilobases, respectively. Each minichromosome has two novel telomeres, as shown by genomic Southern hybridization with an S. pombe telomere probe. Comparison by hybridization of the minichromosomes and their chromosomal counterparts showed no signs of gross rearrangement. Cosmid clones covering the ends of the long arms of Ch16 and Ch12 were isolated, and subcloned fragments that contained the breakage sites were identified. They are apparently unique in the genome. By hybridization and Bal 31 digestion, the ends appear to consist of the broken-end sequences directly associated with short stretches (about 300 base pairs) of new DNA that hybridizes to a cloned S. pombe telomere. They do not contain the telomere-adjacent repeated sequences that are present in the normal chromosomes. The sizes of the short telomeric stretches are roughly the same as those of the normal chromosomes. Our results show that broken chromosomal ends in S. pombe can be healed by the de novo addition of the short telomeric repeats. The formation of Ch16 must have required two breakage-healing events, whereas a single cleavage-healing event in the long arm of Ch16 yielded Ch12.

Chromosomes↗
PubMed1987

Yeast tubulin genes.

There are two alpha-tubulin genes and one beta-tubulin gene in Schizosaccharomyces pombe and Saccharomyces cerevisiae. Detailed analyses employing tubulin mutants and cloned genes have revealed different cellular roles for the tubulin genes in these organisms.

Amino Acid Sequence↗
PubMed1986

Chromosome walking shows a highly homologous repetitive sequence present in all the centromere regions of fission yeast.

By cloning centromere-linked genes followed by partial overlapping hybridization, we constructed a 210-kb map encompassing the centromere in chromosome II and a 60-kp map near the centromere of chromosome I in the fission yeast Schizosaccharomyces pombe which has three chromosomes. Integration of the cloned sequences into the chromosome and subsequent analyses of tetrads and dyads revealed an approximately 50 kb long domain located in the middle of the 210-kb map, tightly linked to the centromere and greatly reduced in meiotic recombination. This domain contained at least two classes of repetitive sequences. One, designated yn1, was specifically present in a particular chromosome and repeated three times in the 210-kb map of chromosome II. The other, designated dg, was located in all the centromere regions of three chromosomes. One (dgI) and two (dgIIa, dgIIb) copies of the dg were found in the maps of chromosomes I and II, respectively. The dgIIa and dgIIb were arranged with a 20-kb interval within the repetitive domain. In the centric region of chromosome II, 3-4 copies of the dg appeared to exist. By determining the nucleotide sequences of dgI and dgIIa, the dg was identified to be 3.8 kb long. The sequence homology was 99% between dgI and dgIIa. These extraordinarily homologous sequences seemed not to be transcribed into RNA nor to be encoding any protein. The larger part of the dg sequence was internally non-repetitious, a 600-bp region existed which consisted of stretches of several short repeating units. The structures in or surrounding the centromeres of S. pombe appear to be much more complex than those of the budding yeast Saccharomyces cerevisiae.

Base Sequence↗
PubMed1986

The nucleotide sequence of the fission yeast DNA topoisomerase II gene: structural and functional relationships to other DNA topoisomerases.

We have determined the complete nucleotide sequence of a 5.3-kb long genomic DNA fragment of the fission yeast Schizosaccharomyces pombe that encodes DNA topoisomerase II. It contains a 4293 bp long single open reading frame. The predicted polypeptide has 1431 residues (mol. wt 162,000) and shows three characteristic domains; the large C-terminal region, which consists of alternating acidic-basic stretches and might be a chromatin-binding domain, the NH2 half domain homologous to the ATP-binding gyrB subunit of bacterial gyrase and the central-to-latter part which is homologous to the NH2 domain of the catalytic gyrA subunit, suggesting a possible evolutionary consequence of the gene fusion of the bacterial gyrase subunits into the eucaryotic DNA topoisomerase II gene. We have found that the cloned fission yeast TOP2 gene can complement the budding yeast top2 mutation, although the fission yeast TOP2 protein sequence is only 50% homologous to the recently determined sequence of budding yeast (J.C. Wang, personal communication). Conversely, the budding yeast TOP2 gene can complement the fission yeast top2 mutations, indicating that their DNA topoisomerase II genes are functionally exchangeable.

Amino Acid Sequence↗
PubMed1986

Isolation and characterization of Schizosaccharomyces pombe cutmutants that block nuclear division but not cytokinesis.

By examining cytological phenotypes of 587 temperature-sensitive mutants of the fission yeast Schizosaccharomyces pombe, we obtained 18 mutants which cause cell division in the absence of nuclear division. By genetic analyses, these novel nuclear division arrest mutants can be classified into nine complementation groups (designated cut1 - cut9). The cytological phenotype of cut mutants is similar but not identical to that of DNA topoisomerase II mutants (top2). The cut1 gene was cloned by transformation and shown to complement cut2 as well as cut1, indicating a functional relationship between the two genes. The cut genes are required for nuclear division, but their mutant phenotypes differ from most of the previously identified mutants which block nuclear division and also the subsequent cytokinesis. Fluorescence microscopy indicates that the mitotic chromosomes formed in cut mutant cells are abnormal and fail to separate properly. We suggest that cut mutations, like top2, block mitotic chromosome formation and concomitantly nuclear division, but that cytokinesis proceeds independently of the defects in nuclear division, demonstrating uncoordinated mitotic pathways. A novel mutant nuc1 is also described which shows a cytological phenotype similar to the double mutant of DNA topoisomerases I and II but contains normal levels of both DNA topoisomerase activities.

Journal Article↗
PubMed1986

Differential expressions of essential and nonessential alpha-tubulin genes in Schizosaccharomyces pombe.

The fission yeast Schizosaccharomyces pombe has two alpha-tubulin genes and one beta-tubulin gene. Gene disruption experiments showed that the alpha 1-tubulin gene (NDA2) is essential whereas the alpha 2 gene is dispensable. The alpha 2-disrupted cells missing alpha 2 transcript and alpha 2 polypeptide could grow and sporulate normally. The alpha 2 gene, however, was expressed in the wild type and the alpha 1 mutant. Alpha 2-Tubulin was distinguished as an electrophoretic band and was assembled into microtubules. The alpha 2-disrupted cells had an increased sensitivity to an antimicrotubule drug thiabendazole, and the alpha 1(cold-sensitive [cs]) alpha 2 (disrupted) cells became not only cs but also temperature sensitive. Northern blot experiments indicated that alpha 2 transcription was minor and constitutive whereas alpha 1 transcription was major and modulated, depending on the gene copy number of the alpha 2 gene. The amounts of alpha 1 and alpha 2 polypeptides estimated by beta-galactosidase activities of the lacZ-fused genes integrated on the chromosome and by intensities of the electrophoretic bands in crude tubulin fractions, however, were comparable, indicating that alpha 2 tubulin is not a minor subtype. We assume that the cells of Schizosaccharomyces pombe have no excess tubulin pool. alpha 1 mutants would then be blocked in the cell cycle because only half the amount of functional alpha-tubulin required for growth can be produced by the alpha 2 gene. On the other hand, the alpha 2-disrupted cells became viable because the synthesis of alpha 1 tubulin was increased by transcriptional or translational modulation or both. The real cause for essential alpha 1 and dispensable alpha 2 genes seems to be in their regulatory sequences instead of the coding sequences.

Gene Expression Regulation↗