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K G Murti

Publications and source records attributed to K G Murti.

At least 37 records · Page 2Linked to original sources
PubMed1997

Elevated expression of the human parainfluenza virus type 1 F gene downregulates HN expression.

Interactions involved in the expression of parainfluenza glycoproteins were examined by expressing cDNA clones of the HN and F genes from human parainfluenza virus type-1 (hPIV1) or Sendai virus (SV) in recombinant Semliki Forest virus (recSFV) or vaccinia-T7 expression vectors. We found that expression of a cloned F protein gene of hPIV1 resulted in downregulation of the HN proteins of hPIV1 or SV. Compared to the amount of HN expressed in the absence of F, coexpression of HN and F led to about 70% reduction in HN. This reduction of HN was observed in both total cell lysates and in protein localized on the cell surface. In contrast to hPIV1 F, SV F did not suppress the expression of HN. Northern blot analysis indicated that similar levels of HN mRNA accumulated in the absence or presence of hPIV1 F. The reduction of HN protein expression by hPIV1 F was detectable after as little as a 10-min labeling period, suggesting that downregulation occurred at the level of translation or at an early stage of protein folding. In hPIV1-infected cells, the amount of F protein synthesized was only about 15% of that of HN, whereas SV F is expressed at high levels. When the level of F in hPIV1-infected cells was artificially increased by recSFV, HN expression was suppressed. The reduction of F protein production in hPIV1-infected cells was regulated at the level of transcription. Characterization of mRNAs produced in hPIV1-infected cells showed that only 20% of the hPIV1 F mRNAs were monocistronic transcripts; 80% were bicistronic M-F readthrough mRNAs. Because proteins are suggested to be synthesized from only the first cistron of bicistronic mRNA in paramyxovirus (T. C. Wong and A. Hirano (1987) J. Virol. 61, 584-589), production of F protein is likely suppressed by transcriptional regulation in hPIV1-infected cells. These results suggest that F is capable of downregulating the synthesis of HN, but that this is normally prevented in hPIV1-infected cells by suppression of F protein synthesis by transcriptional regulation.

Animals↗
PubMed1997

The human homologue of yeast CRM1 is in a dynamic subcomplex with CAN/Nup214 and a novel nuclear pore component Nup88.

The oncogenic nucleoporin CAN/Nup214 is essential in vertebrate cells. Its depletion results in defective nuclear protein import, inhibition of messenger RNA export and cell cycle arrest. We recently found that CAN associates with proteins of 88 and 112 kDa, which we have now cloned and characterized. The 88 kDa protein is a novel nuclear pore complex (NPC) component, which we have named Nup88. Depletion of CAN from the NPC results in concomitant loss of Nup88, indicating that the localization of Nup88 to the NPC is dependent on CAN binding. The 112 kDa protein is the human homologue of yeast CRM1, a protein known to be required for maintenance of correct chromosome structure. This human CRM1 (hCRM1) localized to the NPC as well as to the nucleoplasm. Nuclear overexpression of the FG-repeat region of CAN, containing its hCRM1-interaction domain, resulted in depletion of hCRM1 from the NPC. In CAN-/- mouse embryos lacking CAN, hCRM1 remained in the nuclear envelope, suggesting that this protein can also bind to other repeat-containing nucleoporins. Lastly, hCRM1 shares a domain of significant homology with importin-beta, a cytoplasmic transport factor that interacts with nucleoporin repeat regions. We propose that hCRM1 is a soluble nuclear transport factor that interacts with the NPC.

Amino Acid Sequence↗
PubMed1996

Nuclear bodies of stage 6 oocytes of Rana temporaria contain nucleolar and coiled body proteins.

The genetically inactive stage 6 oocyte nuclei of Rana temporaria contain certain nuclear bodies that label with nucleolus-specific and coiled body (CB)-specific antibodies. We designate them multicomponent bodies (MCBs) to reflect their mixed composition. Morphologically, each MCB contains five distinct zones: zone I composed of electron-dense fibrils similar to the dense fibrillar component (DFC) of the typical eukaryotic nucleoli; zone II resembled the fibrillar material of the inactive agranular nucleoli of stage 6 oocytes; zone III consisted of fine filamentous material corresponding to the fibrillar center (FC) of lower electron density seen in the typical nucleoli; and zones IV and V contained packed coiled threads typical of CBs. Of these, zone IV was seen in the interior of MCBs and contained tightly packed coiled threads (20 nm thick), while zone V occurred at the periphery and consisted of similar threads but loosely packed and electron dense. The material of both zones IV and V resembled that of CBs. To determine the composition of these zones, we extracted oocytes with a buffer that removes chromatin and most of the soluble proteins and processed them for immunogold labeling with a variety of antibodies. Anti-p80 coilin antibody predominantly labeled zone IV and, to a lesser extent, zone V. Anti-snRNP antibody also showed a similar labeling pattern. Anti-fibrillarin antibody predominantly labeled zone I and to a lesser extent zones IV and V. Anti-B23 antibody labeled all zones. These observations suggest that MCBs contain both nucleolar and CB material. We postulate that MCBs represent storage structures which provide material needed for the early stage of embryogenesis. The demonstration of MCBs further supports the close interrelationship between nucleoli and CBs.

Animals↗
PubMed1996

Molecular interactions between human B-cell progenitors and the bone marrow microenvironment.

Apoptosis of normal and leukemic immature B-cells in vitro is suppressed when either cell type is grown in direct contact with a feeder layer of bone marrow-derived stromal cells, including fibroblasts, macrophages, endothelial cells, and adipocytes. In this study, our objective was to identify a stromal cell type which is essential for lymphoblast survival and to characterize the molecules involved in lymphoblast adhesion to these cells. In experiments with B-lineage acute lymphoblastic leukemia (ALL) cells (n = 28) and purified CD19(+) cells from normal bone marrow (n = 6) we found that homogeneous populations of bone marrow fibroblasts could sustain survival of normal and leukemic immature B-cells as efficiently as composite bone marrow stromal layers. Electron microscopic studies showed that leukemic lymphoblasts associate with fibroblasts and with the extracellular matrix (ECM) primarily via their specialized cell surface structures. Immunogold labelingsoliduselectron microscopy analysis revealed that the areas of contact between lymphoblasts and fibroblasts contained beta1 integrins (VLA-4 and VLA-5), fibronectin, vascular cell adhesion molecule (VCAM-1), and a cartilage-link protein, CD44. Double immunogold labeling studies disclosed a direct in situ relationship between fibronectin and VLA-4, VLA-5, and CD44. We hypothesize that these molecular interactions either bring lymphoblasts into close physical proximity with other fibroblast-bound or ECM-bound survival factors or provide survival signals themselves.

B-Lymphocytes↗
PubMed1996

Dynamics of human replication protein A subunit distribution and partitioning in the cell cycle.

Human replication protein A (RPA) is a three-sub-unit protein complex involved in DNA replication, repair, and recombination. To gain insight into the dynamics of subunit assembly, we examined the subcellular distribution of RPA subunits (p70, p34, and p11) during the cell cycle. All three subunits colocalized in G1 and S phases, showing a diffuse nuclear distribution in G1 but a dot-like nuclear pattern in S phase. During S phase, the subunits showed a pattern reminiscent of the replication granules/factories described by others as sites of replication machinery. In meta-phase, p70 preferentially associated with the spindle poles, p34 was found on chromosomes, and p11 remained in the cytoplasm. In telophase, p70 and p34 appeared in the forming daughter nuclei; p11 remained in the cytoplasm until G1. Among the three subunits only p34 was associated with the nuclear matrix and this association persisted throughout the cell cycle. We conclude that (i) RPA complex assembly is differentially regulated, (ii) the replication machinery may be anchored to the nuclear matrix, and (iii) RPA subunits partition during mitosis and sort into daughter nuclei by different routes.

Cell Cycle↗
PubMed1996

The cytoplasmic tail of influenza A virus neuraminidase (NA) affects NA incorporation into virions, virion morphology, and virulence in mice but is not essential for virus replication.

In this study, we investigated the role of the conserved neuraminidase (NA) cytoplasmic tail residues in influenza virus replication. Mutants of influenza A virus (A/WSN/33 [H1N1]) with deletions of the NA cytoplasmic tail region were generated by reverse genetics. The resulting viruses, designated NOTAIL, contain only the initiating methionine of the conserved six amino-terminal residues. The mutant viruses grew much less readily and produced smaller plaques than did the wild-type virus. Despite similar levels of NA cell surface expression by the NOTAIL mutants and wild-type virus, incorporation of mutant NA molecules into virions was decreased by 86%. This reduction resulted in less NA activity per virion, leading to the formation of large aggregates of progeny mutant virions on the surface of infected cells. A NOTAIL virus containing an additional mutation (Ser-12 to Pro) in the transmembrane domain incorporated three times more NA molecules into virions than did the NOTAIL parent but approximately half of the amount incorporated by the wild-type virus. However, aggregation of the progeny virions still occurred at the cell surface. All NOTAIL viruses were attenuated in mice. We conclude that the cytoplasmic tail of NA is not absolutely essential for virus replication but exerts important effects on the incorporation of NA into virions and thus on the aggregation and virulence of progeny virus. In addition, the relative abundance of long filamentous particles formed by the NOTAIL mutants, compared with the largely spherical wild-type particles, indicates a role for the NA cytoplasmic tail in virion morphogenesis.

Amino Acid Sequence↗
PubMed1996

Characterization of mutants of influenza A virus selected with the neuraminidase inhibitor 4-guanidino-Neu5Ac2en.

The development of viral resistance to the neuraminidase (NA) inhibitor, 4-guanidino-Neu5Ac2en, of influenza viruses was studied by serial passage of A/Turkey/Minnesota/833/80 (H4N2) in Madin-Darby canine kidney cells in the presence of increasing concentrations of inhibitor. Resistant mutants selected after eight passages, had a 10,000-fold reduction in sensitivity to the inhibitor in plaque assays, but their affinity (1/Kd) to the inhibitor was similar to that of the parental virus. Electron microscopic analysis revealed aggregation of the mutant virus at the cell surface in the presence of the inhibitor. Sequence analysis established that a substitution had occurred in the NA (Arg-249 to Lys) and in the HA2 subunit of the hemagglutinin (Gly-75 to Glu), in the vicinity of the proposed second sialic acid binding site. The change of residue 249 appears to be a chance mutation, for we were unable to reisolate this mutant, whereas subsequent experiments indicate changes in the hemagglutinin. After 13 passages of the parental virus, mutants that were resistant to the high concentrations of inhibitor tested were obtained. These viruses retained their drug-resistant phenotype even after five passages without the inhibitor. Electron microscopic analysis revealed no aggregation of virus on the surface of infected cells in the presence of the inhibitor. Sequence analysis of the NA gene from these drug-resistant mutants revealed an additional substitution of Glu to Ala at the conserved amino acid residue 119. This substitution is responsible for reducing the affinity of the inhibitor to the NA. Our findings suggest that the emergence of mutants resistant to 4-guanidine-Neu5Ac2en is a multistep process requiring prolonged exposure to the inhibitor.

Animals↗
PubMed1996

Human B-cell progenitors and bone marrow microenvironment.

Apoptosis of normal and leukemic immature B-cells in vitro is suppressed by contact with bone marrow-derived stromal layers. In stroma-supported cultures of immature B-cells, we found that ligation of CD38, a type II transmembrane protein, inhibited the cell growth and induced apoptosis. CD38 ligation also induced tyrosine phosphorylation and activation of intracellular substrates, including syk, phospholipase C-gamma, c-cbl, and phosphatidylinositol 3-kinase (PI 3-K). Wortmannin and LY294002, two potent inhibitors of PI 3K, rescued immature B cells from CD38-mediated growth suppression. In vitro culture of leukemic lymphoblasts may have potentially important clinical application. First, stroma-supported cultures of acute lymphoblastic leukemia (ALL) cells can determine the growth potential of leukemic cells. In a series of 70 children enrolled in a single program of chemotherapy, cell growth on stroma was a powerful and independent prognostic indicator. Second, a culture system capable of maintaining the majority of ALL blast cells at high levels of viability is also ideally suited for testing antileukemic drugs. Promising results were obtained with 2-chloro-deoxyadenosine and interleukin-4, leading to clinical trials of these two compounds in children with refractory ALL. In addition, we compared the direct antileukemic activities of dexamethasone and prednisolone and found that dexamethasone is five to six times more cytotoxic (on a molar basis) than prednisolone, in agreement with the anti-inflammatory activities of these drugs. This finding may serve to guide the selection of dexamethasone dosage in the treatment of ALL.

ADP-ribosyl Cyclase↗
PubMed1995

Relocation of the carboxyterminal part of CAN from the nuclear envelope to the nucleus as a result of leukemia-specific chromosome rearrangements.

Fusion genes encoding the 3' part of the can gene are implicated in two types of leukemia. The dek-can fusion gene is present in t(6;9) acute myeloid leukemia and the set-can fusion gene is present in one case of acute undifferentiated leukemia. In order to obtain leads towards the molecular basis of these diseases, we have studied the cellular localization of the DEK-CAN and SET-CAN fusion proteins and their normal counterparts. DEK-CAN and SET-CAN were localized exclusively in the nucleus, and also DEK and SET were found to be nuclear proteins. However, CAN was mainly located at the nuclear and cytoplasmic face of the nuclear envelope. This observation is in accordance with the presence of an amino acid repeat in the C-terminal part of CAN, common to the family of nucleoporins. The C-terminal part also contains a nuclear location domain as shown by deletion analysis. This domain may be important for the presence of CAN at the nucleoplasmic side of the nuclear envelope. The relocation of the carboxyterminal part of CAN due to DEK-CAN and SET-CAN may reinforce a nuclear function of the CAN protein.

Acute Disease↗
PubMed1995

Ligation of CD38 suppresses human B lymphopoiesis.

CD38 is a transmembrane glycoprotein expressed in many cell types, including lymphoid progenitors and activated lymphocytes. High levels of CD38 expression on immature lymphoid cells suggest its role in the regulation of cell growth and differentiation, but there is no evidence demonstrating a functional activity of CD38 on these cells. We used stroma-supported cultures of B cell progenitors and anti-CD38 monoclonal antibodies (T16 and IB4) to study CD38 function. In cultures of normal bone marrow CD19+ cells (n = 5), addition of anti-CD38 markedly reduced the number of cells recovered after 7 d. Cell loss was greatest among CD19+ sIg- B cell progenitors (mean cell recovery +/- SD = 7.2 +/- 11.7% of recovery in control cultures) and extended to CD19+CD34+ B cells (the most immature subset; 7.6 +/- 2.2%). In contrast, CD38 ligation did not substantially affect cell numbers in cultures of normal peripheral blood or tonsillar B cells. In stroma-supported cultures of 22 B-lineage acute lymphoblastic leukemia cases, anti-CD38 suppressed recovery of CD19+ sIg- leukemic cells. CD38 ligation also suppressed the growth of immature lymphoid cell lines cultured on stroma and, in some cases, in the presence of stroma-derived cytokines (interleukin [IL] 7, IL-3, and/or stem cell factor), but did not inhibit growth in stroma- or cytokine-free cultures. DNA content and DNA fragmentation studies showed that CD38 ligation of stroma-supported cells resulted in both inhibition of DNA synthesis and induction of apoptosis. It is known that CD38 catalyzes nicotinamide adenine dinucleotide (NAD+) hydrolysis into cyclic ADP-ribose (cADPR) and ADPR. However, no changes in NAD+ hydrolysis or cADPR and ADPR production after CD38 ligation were found by high-performance liquid chromatography; addition of NAD+, ADPR, or cADPR to cultures of lymphoid progenitors did not offset the inhibitory effects of anti-CD38. Thus, anti-CD38 does not suppress B lymphopoiesis by altering the enzymatic function of the molecule. In conclusion, these data show that CD38 ligation inhibits the growth of immature B lymphoid cells in the bone marrow microenvironment, and suggest that CD38 interaction with a putative ligand represents a novel regulatory mechanism of B lymphopoiesis.

ADP-ribosyl Cyclase↗
PubMed1995

Nuclear actin filaments and their topological changes in frog oocytes.

Previous morphological and biochemical studies have suggested that actin and actin-containing filaments (microfilaments) exist in the eukaryotic nucleus and that they perform important nuclear functions. However, the concept is not widely accepted. In this study, we demonstrate actin and bundles of actin in the nuclei of oocytes of Rana temporaria by immunoblotting and immunogold labeling/electron microscopy. The system and methods used here provided nuclei, free from cytoplasmic contamination. Additionally, we have compared the topological distribution of intranuclear actin filaments in two structurally and functionally distinct stages (stages 3 and 6) of oogenesis. The stage 3 nuclei are extremely active in rRNA transcription and contain multiple nucleoli located at the periphery with the central part occupied by the lampbrush chromosomes. The stage 6 nuclei are transcriptionally inert and contain both nucleoli and chromosomes confined to a small area in the central part. The nuclear lysates derived from the manually isolated stage 3 and 6 nuclei and the nuclear contents obtained by manually removing the nuclear envelope of stage 6 nucleus both contained actin as demonstrated by immunoblotting with an actin-specific monoclonal antibody. When examined by immunogold electron microscopy using the anti-actin antibody, the stage 3 oocyte nuclei showed distinct intranuclear tracks composed of bundles of actin that extended from the nucleoli and chromosomes to the nuclear envelope. The stage 6 oocyte nuclei, on the other hand, showed short stretches of actin bundles in the central part mainly in association with the nucleoli; none of these bundles extended to the nuclear envelope. Taken together, the above results suggest that actin is a structural component of the oocyte nucleus and that polymerized actin undergoes dramatic topological changes correlated with changes in the distribution of nuclear components and their function.

Actins↗
PubMed1995

In vivo expression of mammalian BiP ATPase mutants causes disruption of the endoplasmic reticulum.

BiP possesses ATP binding/hydrolysis activities that are thought to be essential for its ability to chaperone protein folding and assembly in the endoplasmic reticulum (ER). We have produced a series of point mutations in a hamster BiP clone that inhibit ATPase activity and have generated a species-specific anti-BiP antibody to monitor the effects of mutant hamster BiP expression in COS monkey cells. The enzymatic inactivation of BiP did not interfere with its ability to bind to Ig heavy chains in vivo but did inhibit ATP-mediated release of heavy chains in vitro. Immunofluorescence staining and electron microscopy revealed vesiculation of the ER membranes in COS cells expressing BiP ATPase mutants. ER disruption was not observed when a "44K" fragment of BiP that did not include the protein binding domain was similarly mutated but was observed when the protein binding region of BiP was expressed without an ATP binding domain. This suggests that BiP binding to target proteins as an inactive chaperone is responsible for the ER disruption. This is the first report on the in vivo expression of mammalian BiP mutants and is demonstration that in vitro-identified ATPase mutants behave as dominant negative mutants when expressed in vivo.

Adenosine Triphosphatases↗
PubMed1995

Expression of the proto-oncogene rhombotin-2 is identical to the acute phase response protein metallothionein, suggesting multiple functions.

Rhombotin-2 (RBTN-2) is a LIM domain protein that, with the exception of thymocytes, is widely expressed during fetal development. Although RBTN-2 is crucial for normal erythropoiesis, the ectopic expression of RBTN-2 in T lymphocytes results in T-cell proliferation and leukemogenesis. Thus, while a proliferative function for RBTN-2 has been established in T-cells, neither its role in erythropoiesis nor its function(s) in other tissues are known. We have examined the expression and location of RBTN-2 in normal and malignant cells. Similar to fetal development, RBTN-2 RNA was detected in all normal adult tissues tested with the exception of colon and thymocytes. RBTN-2 RNA was not detected in all primary tumors and tumor cell lines, indicating RBTN-2 expression is not ubiquitous in proliferating cells. Using polyclonal antisera, RBTN-2 was detected predominantly in the nucleus of human hematopoietic cells. Significantly, human leukemic T cells with disruption of the RBTN-2 locus and thymocytes from transgenic mice with enforced expression of RBTN-2 showed similar nuclear location of RBTN-2 protein, consistent with the notion that RBTN-2 acts as a transcriptional regulator in T-cell proliferation. Surprisingly, in normal tissues, RBTN-2 showed a strikingly similar distribution to that of metallothionein-1, having both nuclear and cytoplasmic localization that suggested that RBTN-2 may be involved in the acute phase response. Indeed, similar to metallothionein-1, RBTN-2 mRNA was induced in thymocytes of mice exposed to zinc and in human thymocytes treated with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate. Since the LIM domain permits binding of multiple protein partners, the specific function of RBTN-2 may depend upon subcellular sequestration through interaction with different cofactors. Thus, in addition to its roles in erythropoiesis and T-cell leukemia, RBTN-2 may also be involved in the acute phase response.

Acute-Phase Proteins↗
PubMed1994

Abortive replication of influenza virus A/WSN/33 in HeLa229 cells: defective viral entry and budding processes.

Since influenza A virus replication is defective in HeLa229 cells but productive in Madin-Darby canine kidney (MDCK) cells, we have investigated the steps in the infectious cycle of A/WSN/33 virus defective in HeLa229 cells. We find that both the entry and exit processes of the infectious cycle were defective in HeLa229 cells. During entry, viral adsorption was apparently normal in HeLa229 cells but a subsequent step(s) involving one or more processes namely the fusion/uncoating and nuclear transport of viral ribonucleoprotein was inefficient and slow compared to those in MDCK cells. Fewer HeLa229 cells were infected at the same multiplicities of infection, resistance to ammonium chloride developed much more slowly and degradation of the incoming virus proteins was delayed when compared to those in MDCK cells. Subsequent to the entry process, there was no significant difference in either the synthesis of viral proteins or the transport, maturation, and membrane insertion of viral glycoproteins although the glycosylation pattern of hemagglutinin was different and the peak protein synthesis was albeit delayed in HeLa229 cells compared to that in MDCK cells. However, there was a major defect in the budding and release of viral particles. In HeLa229 cells, viral bud formation occurred but viral particles remained attached to the plasma membrane and were not released into the medium. This defect in virus release was not due to lack of neuraminidase activity but could be, at least partly, overcome by cytochalasin B treatment, suggesting a possible involvement of microfilaments in virus release. These results indicate that the abortive replication of influenza virus A/WSN/33 in HeLa229 cells appears to be due to multiple defects involving both the entry and release of viral particles and that host cell membrane and microfilaments may be important contributing factors in these processes.

Animals↗
PubMed1994

Adhesion-dependent survival of normal and leukemic human B lymphoblasts on bone marrow stromal cells.

We investigated the requirement for intimate contact between bone marrow stroma and B lymphoblasts from normal donors and children with leukemia. By scanning electron microscopy, both normal and leukemic cells seeded onto stroma were surrounded by folds of stromal cells or were linked to the stroma by fine tendrils and uropods. Separation of normal B progenitors from stroma by use of microporous membranes led to significantly lower cell recoveries compared with results when contact was unimpeded. For instance, 22.5% +/- 1.8% (mean +/- SEM) of CD19+, CD34+ cells (most immature subset) were recovered after a 7-day culture directly on stroma, compared with 5.2% +/- 0.7% after growth on membranes (P < .001 by Student's t test). In 6 of 11 cases of B-lineage acute lymphoblastic leukemia, separation of progenitors from stroma resulted in apoptosis and a greater than 60% reduction in cell recovery. In the remaining 5 cases, however, this effect was much less pronounced, with reductions in cell recoveries ranging from 48.5% to less than 1% (median, 39.0%) of control values. Inhibition of very late antigen-4, a surface molecule critical for adhesion of B lymphoblasts to stroma, was associated with a greater loss of normal CD34+ B progenitors compared with that for equivalent leukemic cells. These results establish direct contact with stroma as a survival requirement of normal B lymphoblasts and show marked heterogeneity in stromal dependency among B-lineage leukemic cells.

Adolescent↗
PubMed1993

Highly localized tracks of human immunodeficiency virus type 1 Nef in the nucleus of cells of a human CD4+ T-cell line.

A human T-cell line constitutively expressing the nef gene from the human immunodeficiency virus type 1 SF2 isolate was used to examine the distribution of the Nef protein in the nucleus. High-resolution immunogold labeling/electron microscopic studies with polyclonal anti-Nef antibodies on nef+ and nef- cells revealed that a small fraction of Nef is in the nucleus and it is localized in specific curvilinear tracks that extend between the nuclear envelope and the nucleoplasm. An examination of the sequence of the SF2 nef gene revealed a putative nuclear targeting sequence that was previously found in several other eukaryotic nucleoplasmic proteins. The nuclear localization of Nef suggests a potential nuclear function for this protein. The presence of Nef in distinct nuclear tracks suggests that Nef is transported along a specific pathway that extends from the nuclear envelope into the nucleoplasm. A previous study [Meier, U. T. & Blobel, G. (1992) Cell 70, 127-138] has shown that the nucleolar protein of rat liver cells (Nopp140) shuttles from the nucleolus to the nuclear envelope on distinct tracks. The present study has suggested that the transport of a nucleoplasmic protein may also occur on distinct nuclear pathways.

Amino Acid Sequence↗
PubMed1993

Crystals of hemagglutinin-neuraminidase of parainfluenza virus contain triple-stranded helices.

When purified dimers of hemagglutinin-neuraminidase molecules released by protease digestion from three strains of human parainfluenza virus 1 were used in crystallization trials, long thin needle crystals formed. Electron microscopic analysis of these needle crystals revealed that they are composed of stacks of triple-stranded helices with each strand of the helix made up of subunits of hemagglutinin-neuraminidase. To our knowledge, this is the first direct demonstration of the assembly of protein subunits into large triple-stranded helices. An understanding of the organization of these triple helices may shed light on the structural properties of the hemagglutinin-neuraminidase molecules that cause them to form these helices.

Crystallization↗