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I Raska

Publications and source records attributed to I Raska.

86 records · Page 5Linked to original sources
PubMed1976

Structure of plain and complex flagellar hooks of Pseudomonas rhodos.

The proximal hooks of plain and complex flagella produced by a strain of Pseudomonas rhodos have been analyzed by electron microscopy and optical diffraction and filtering. Plain flagellar hooks are cone-shaped, 70 nm long, and 13 to 21.5 nm wide, and consist of helically arranged subunits. Complex flagellar hooks are cylinders, 180 to 190 nm long, and 15 to 16 nm wide, and are composed of globular subunits. The structure comprises four small-scale helical rows of subunits intersecting bewteen 10 and 11 large-scale helices of pitch angle 80 degrees. The axial and lateral dimensions of the unit cell, which define the surface lattice, are 4.9 and 4.7 nm, respectively. In addition, a core structure, approximately 5 nm wide, has been demonstrated inside the hook cylinder. Complex flagellar hooks were isolated and purified by gradient centrifugation after acid degradation of the attached filaments. Isolated hook particles have an average sedimentation constant of 130S and consist of a protein of molecular weight 43,000. A model of the complex flagellar hook is presented, and its possible role in flagellar assembly and rotation is discussed.

Flagella↗
PubMed1974

Plain and complex flagella of Pseudomonas rhodos: analysis of fine structure and composition.

Cells of Pseudomonas rhodos 9-6 produce two morphologically distinct flagella termed plain and complex, respectively. Fine structure analyses by electron microscopy and optical diffraction showed that plain flagellar filaments are cylinders of 13-nm diameter composed of globular subunits like normal bacterial flagella. The structure comprises nine large-scale helical rows of subunits intersecting four small-scale helices of pitch angle 25 degrees . Complex filaments have a conspicuous helical sheath, 18-nm wide, of three close-fitting helical bands, each about 4.7-nm wide, separated by axial intervals, 4.7 nm wide, running at an angle of 27 degrees . The internal core has similar but not identical substructure to plain filaments. Unlike plain flagella, the complex species is fragile and does not aggregate in bundles. Mutants bearing only one of two types of flagellum were isolated. Cells with plain flagella showed normal translational motion, and cells with complex flagella showed rapid spinning. Isolated plain flagella consist of a 37,000-dalton subunit separable into two isoproteins. Complex filaments consist of a 55,000-dalton protein; a second 43,000-dalton protein was assigned to complex flagellar hooks. The results indicate that plain and complex flagella are entirely different in structure and composition and that the complex type represents a novel flagellar species. Its possible mode of action is discussed.

Bacterial Proteins↗
PubMedDate not supplied

Does the synthesis of ribosomal RNA take place within nucleolar fibrillar centers or dense fibrillar components? A critical appraisal.

The localization of transcribing rRNA genes within nucleoli of mammalian cells, although intensively studied, has not been established. Most published papers on this topic situate transcribing ribosomal genes either to nucleolar fibrillar centers or to nucleolar dense fibrillar components. To clarify this point, we have generated the electron microscopic affinity cytochemistry picture of the nucleolus of cultured mammalian cells. Three kinds of affinity probes have been used: (1) probes to nucleolar chromatin, including rDNA sequences; (2) probes to a number of macromolecules (such as RNA polymerase I) which are directly, or indirectly, involved in the synthesis and processing of rRNA and formation of preribosomes; (3) antibodies to bromouridine for a recently standardized nonisotopical method depicting incorporated bromouridine within RNA. The results suggest the localization of transcription sites not only to dense fibrillar components but also to the border region between these components and fibrillar centers. Our data support a hypothesis that in metabolically active mammalian nucleoli, fibrillar centers and dense fibrillar components form a single functional domain for the transcription of rRNA genes, with nascent transcripts generating "automatically" dense fibrillar components. Through the active process of transcription, individual rRNA genes thus become engulfed within dense fibrillar components.

3T3 Cells↗
PubMedDate not supplied

Ultrastructural nonisotopic mapping of nucleolar transcription sites in onion protoplasts.

The post- and preembedding ultrastructural localization of transcribing rRNA genes has been carried out in nucleoli of permeabilized onion growing root tip protoplasts by means of the nonisotopic bromouridine method. By means of both post- and preembedding approaches, major synthetic sites were identified with morphologically distinct subdomains of dense fibrillar components, with some signal also being associated with nucleolar fibrillar centers and vacuoles. Moreover, labeled medusoid fibrils within distinct domains seen in Lowicryl thin sections likely represent the morphological correlate of transcribing nucleolar genes.

Allium↗
PubMedDate not supplied

Structural organization of the pre-mRNA splicing commitment: a hypothesis.

Several models have been presented in the past to explain localized distributions of nuclear RNAs from individual genes that range from small foci to more elongated "track-like" structures. We present here a hypothesis which explains that, in the case of regulated splicing, there is in diploid cells a spatial separation of transcription sites from the execution of regulated splicing which we situate to domains of SR protein accumulation. In addition, it explains the presence of poly(A) sequences, and the lack of the autoradiographic label due to short pulses of [3H]uridine, in these domains.

Animals↗
PubMedDate not supplied

Association between the nucleolus and the coiled body.

By means of light and electron microscopic immunocytochemistry, we have localized p80-coilin, a specific protein marker for coiled bodies, in mammalian cell lines as well as in primary rat neuron cultures. p80-coilin-stained nuclear bodies, which also contained fibrillarin, could be subsequently silver stained by a method specific for the visualization of nucleolar organizer regions. In cycling cells, most coiled bodies were not associated with nucleoli, whereas in rat neurons such as association was frequent. The treatment of cycling cells with actinomycin D or 5,6-dichloro-1-beta-D-ribo furanosyl-benzimidazole led to nucleolar segregation and/or disintegration, and to an association of p80-coilin staining structures with nucleoli. p80-coilin-positive structures contained fibrillarin in both untreated and treated cells. These results support the opinion that there might be a special association between coiled bodies and nucleoli, particularly in neuronal cells.

Animals↗
PubMedDate not supplied

Cyclin D-cdk6 complex is targeted by p21(WAF) in growth-arrested lymphoma cells.

Normal human B lymphocytes are sensitive to the growth-inhibitory action of transforming growth factor beta1 (TGFbeta1) whereas malignant B lymphoma cells are mostly resistant to TGFbeta1 effects. We examined the phosphorylation status of retinoblastoma protein and the activity of G(1) cyclin-dependent kinases (cdk) in TGFbeta1-sensitive malignant follicular lymphoma cells during the TGFbeta1 treatment. The kinase activity of cdk2, cdk4, and cdk6 was significantly reduced and hypophosphorylation of pRb on serine 795 (S795) and threonine 373 (T373) was observed. We examined the composition of cdk complexes and the level of cdk inhibitors to explain the inhibitory action of TGFbeta1 toward cdk activity. Both cdk4 and cdk6 were notably dissociated from cyclin D cofactors, while cyclin E-cdk2 complexes remained coupled in TGFbeta1-treated cells. TGFbeta1-induced growth arrest was associated with notably increased binding of p21(WAF1) to cdk4 and cdk6. No induction of cdk-inhibitor molecules of INK family was observed in TGFbeta1-treated DoHH2 cells. As shown, TGFbeta1-induced growth arrest of malignant B cells was associated with the activation of CIP/KIP family members of cdk inhibitors.

Blotting, Western↗
PubMedDate not supplied

Non-isotopic detection of nucleolar transcription in pre-implantation mouse embryos.

Nucleolar transcription was analysed in permeabilized pre-implantation mouse embryos at the four-cell, eight-cell, morula and early blastocyst stages using confocal microscopy to detect incorporated 5-bromouridine. The results demonstrated that the patterns of nucleolar transcription sites were common for all embryonic stages studied. They consisted most frequently of tightly associated groups of transcription foci similar to those encountered in somatic interphase cells. In addition, the nucleologenesis accompanying each cell cycle apparently gave rise to a different fluorescent pattern, that is to spatially separated fluorescent foci in the cells just after the resumption of rRNA synthesis. An immunoelectron microscopic analysis of the nucleolar transcription was also performed in the eight-cell embryos. A signal, usually consisting of clustered gold particles, was found specifically within nucleolar dense fibrillar components. This result was in agreement with established findings, which identify dense fibrillar component as the major site of nucleolar transcription in somatic cells.

Animals↗