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Biomedical subjects

N Larsen

Publications and source records attributed to N Larsen.

15 recordsLinked to original sources
PubMed1992

Higher order interactions in 23s rRNA.

An alignment of 75 phylogenetically diverse large subunit ribosomal RNA sequences was created and searched for secondary and tertiary structure elements by computer. The search revealed four unknown secondary structural pairings, two internal loop closings, and five short-range tertiary interactions--two of which were pairings of an unusual type. One brings a loop together with two other loops previously known to be paired, and one involves a nucleotide within a presumed tetraloop. The latter interaction constrains the RNA structure near the ribosomal E-site, where two base pairs previously suggested to be in parallel orientation are now proven. No clear phylogenetic evidence for direct base pairing between the large and small subunit rRNA was found.

Base Sequence↗
PubMed1992

The Ribosomal Database Project.

The Ribosomal Database Project (RDP) complies ribosomal sequences and related data, and redistributes them in aligned and phylogenetically ordered form to its user community. It also offers various software packages for handling, analyzing and displaying sequences. In addition, the RDP offers (or will offer) certain analytic services. At present the project is in an intermediate stage of development.

Base Sequence↗
PubMed1991

SRP-RNA sequence alignment and secondary structure.

The secondary structures of the RNAs from the signal recognition particle, termed SRP-RNA, were derived buy comparative analyses of an alignment of 39 sequences. The models are minimal in that only base pairs are included for which there is comparative evidence. The structures represent refinements of earlier versions and include a new short helix.

Archaea↗
PubMed1991

Archaeal rRNA operons.

Ribosomal RNA (rRNA) operons of the archaea reflect both the unity and the diversity of this third primary taxon. They have proven to be a rich source of both molecular biological and phylogenetic information.

Archaea↗
PubMed1990

[First aid, prehospitalization treatment, performed by non-professionals].

In the Casualty Department of the Central Hospital in Slagelse, all acute referrals during a period of 48 hours (illness or accidents) were registered with the object of assessing the extent to which lay persons employ first-aid. First-aid had been employed in half of the cases investigated but was considered relevant in 82% of the cases. The circumstances associated with performance of first-aid are discussed and proposals are made for improvement.

Adolescent↗
PubMed1989

The 23S ribosomal RNA higher-order structure of Pseudomonas cepacia and other prokaryotes.

A 23S ribosomal RNA gene of Pseudomonas cepacia has been cloned and sequenced. A general higher-order structure model based on earlier published models has been derived from comparative analysis of 23S-like rRNAs of eubacteria, archaebacteria, organelles and eukaryotes. Differences between the previous models were carefully analyzed and controversial regions evaluated. Moderately large insertions and deletions have been found at new points in the secondary structure. The analysis of 50 published as well as unpublished 23S rRNA sequences provide additional proof for six of the seven previously suggested tertiary interactions within the 23S rRNA. P. cepacia is the first representative of the beta subgroup of the Proteobacteria phylum whose 23S rRNA has been sequenced. A tree reflecting evolutionary relationships of prokaryotes was constructed. The topology of this tree is in good agreement with the 16S rRNA tree.

Base Sequence↗
PubMed1989

Protein L18 binds primarily at the junctions of helix II and internal loops A and B in Escherichia coli 5 S RNA. Implications for 5 S RNA structure.

Ribonuclease and chemical probes were used to investigate the binding sites of ribosomal protein L18 on Escherichia coli 5 S RNA using both end-labelling and reverse transcriptase procedures. The results, together with earlier data, were superimposed on a cylindrical projection of RNA double helices and most of the protection effects were found to cluster in the major groove at two sites located on one side of the RNA at the junctions of helix II with the adjoining internal loops A and B. The loop A/helix II junction was investigated using 5 S RNA mutants, produced by site-directed mutagenesis, that exhibited altered binding properties to L18. These results, together with those from a circular dichroism study of L18 complexed with the wild-type and different mutant RNAs, enabled us to assign an L18-induced conformational change to loop A. We infer that this change contributes to the co-operative binding of L5 to helix I, which may be reinforced by the binding of the very basic N-terminal peptide of L18 within the minor groove of helix I. A psoralen derivative formed a mono-addition product with U25 within loop B in the free RNA but not in the L18 complex. Moreover, the modified molecules were selected against in L18 binding experiments. Protection effects that occurred within the adjoining helix III and loop C were compatible with a tertiary interaction between loop C and loop B/helix III that could be stabilized by the L18 binding to the junction of helix II and loop B. Further support for a bipartite binding site derived from the finding that ethidium bromide molecules that are displaced from E. coli 5 S RNA by L18 intercalate both at the loop A/helix II junction and in loop B at the binding site of the psoralen derivative.

Bacterial Proteins↗
PubMed1989

Phylogenetic relationships of the green alga Volvox carteri deduced from small-subunit ribosomal RNA comparisons.

The 1788-nucleotide sequence of the small-subunit ribosomal RNA (srRNA) coding region from the chlorophyte Volvox carteri was determined. The secondary structure bears features typical of the universal model of srRNA, including about 40 helices and a division into four domains. Phylogenetic relationships to 17 other eukaryotes, including two other chlorophytes, were explored by comparing srRNA sequences. Similarity values and the inspection of phylogenetic trees derived by distance matrix methods revealed a close relationship between V. carteri and Chlamydomonas reinhardtii. The results are consistent with the view that these Volvocales, and the third green alga, Nanochlorum eucaryotum, are more closely related to higher plants than to any other major eukaryotic group, but constitute a distinct lineage that has long been separated from the line leading to the higher plants.

Animals↗
PubMed1989

Pulmonary hypoplasia and osteogenesis imperfecta type II with defective synthesis of alpha I(1) procollagen.

Perinatal lethal osteogenesis imperfecta (OI type II), a heritable disorder of connective tissue occurs approximately once in 60,000 live births. Phenotypic characteristics include defective cranial ossification and severe skeletal deformity due to intrauterine rib and long bone fractures. Lethal OI may be associated with intracranial hemorrhage or severe respiratory insufficiency. Pulmonary hypoplasia has been previously observed in OI type II, but has not been defined clinically. The infant described herein was born with OI type II and pulmonary hypoplasia. Pathological examination of airway branching patterns indicated that lung development had progressed to only the 10 week stage with immature acinar development. Investigation type I collagen synthesis by cultured dermal fibroblasts revealed the presence of electrophoretically abnormal alpha 1(I) polypeptides. These findings suggest that biochemically regulated processes, as well as mechanical factors, may impeded pulmonary development in similar cases of OI type II.

Culture Techniques↗
PubMed1988

Immunological typing of acute leukemias: immunoenzymatic staining of fixed cells compared with immunofluorescence staining of unfixed cells in suspension.

A panel of 14 monoclonal antibodies (McAb) against hematopoietic cell surface antigens was applied on mononuclear blood or bone marrow cells from 40 cases of acute leukemia in order to compare immunoenzymatic staining (IE) (alkaline phosphatase) of fixed cells with immunofluorescence staining (IF) of unfixed suspended cells. According to the immunological results, 25 cases were phenotyped as ALL and 15 cases as AML. Cases with blast crisis secondary to chronic myelogenous leukemia (CML-BC) were not represented in this series. In all ALL cases the two methods gave an identical antigenic distribution. In 20 our of 21 cases of non-T-cell ALL, a B-cell progenitor origin was demonstrated by a positive staining reaction with the anti-CD19 McAb AB1 or HD37, and in 10 cases additionally with the anti-CD20 McAb B1 or 1F5. In contrast to the results obtained with IF, IE revealed a poor preservation of the AB1 epitope on CD19, whereas the HD37 epitope was equally well demonstrated by both methods. In 15 cases of AML the distribution of positive versus negative cells with IE or IF was identical for all McAb except J5 (anti-CALLA) (CD10) and B1 (CD20). Thus, 10/15 AML cases expressed CALLA with IE compared to 2/15 with IF. The corresponding figures for B1 were 5/15 and 0/15, respectively. Accordingly, normal myeloid precursor cells were CALLA-positive with IE but negative with IF. The discrepancy probably reflects the fact that, whereas both intracytoplasmatic and membrane-bound antigens are exposed in IE, only the latter are in IF. If the alteration of antigenic accessibility after fixation is considered, IE can safely be used for immunophenotyping of acute leukemia.

Antibodies, Monoclonal↗
PubMed1987

Evolutionary relationships amongst archaebacteria. A comparative study of 23 S ribosomal RNAs of a sulphur-dependent extreme thermophile, an extreme halophile and a thermophilic methanogen.

The 23 S RNA genes representative of each of the main archaebacterial subkingdoms, Desulfurococcus mobilis an extreme thermophile, Halococcus morrhuae an extreme halophile and Methanobacterium thermoautotrophicum a thermophilic methanogen, were cloned and sequenced. The inferred RNA sequences were aligned with all the available 23 S-like RNAs of other archaebacteria, eubacteria/chloroplasts and the cytoplasm of eukaryotes. Universal secondary structural models containing six major structural domains were refined, and extended, using the sequence comparison approach. Much of the present structure was confirmed but six new helices were added, including one that also exists in the eukaryotic 5.8 S RNA, and extensions were made to several existing helices. The data throw doubt on whether the 5' and 3' ends of the 23 S RNA interact, since no stable helix can form in either the extreme thermophile or the methanogen RNA. A few secondary structural features, specific to the archaebacterial RNAs were identified; two of these were supported by a comparison of the archaebacterial RNA sequences, and experimentally, using chemical and ribonuclease probes. Seven tertiary structural interactions, common to all 23 S-like RNAs, were predicted within unpaired regions of the secondary structural model on the basis of co-variation of nucleotide pairs; two lie in the region of the 23 S RNA corresponding to 5.8 S RNA but they are not conserved in the latter. The flanking sequences of each of the RNAs could base-pair to form long RNA processing stems. They were not conserved in sequence but each exhibited a secondary structural feature that is common to all the archaebacterial stems for both 16 S and 23 S RNAs and constitutes a processing site. Kingdom-specific nucleotides have been identified that are associated with antibiotic binding sites at functional centres in 23 S-like RNAs: in the peptidyl transferase centre (erythromycin-domain V) the archaebacterial RNAs classify with the eukaryotic RNAs; at the elongation factor-dependent GTPase centre (thiostrepton-domain II) they fall with the eubacteria, and at the putative amino acyl tRNA site (alpha-sarcin-domain VI) they resemble eukaryotes. Two of the proposed tertiary interactions offer a structural explanation for how functional coupling of domains II and V occurs at the peptidyl transferase centre. Phylogenetic trees were constructed for the archaebacterial kingdom, and for the other two kingdoms, on the basis of the aligned 23 S-like RNA sequences.(ABSTRACT TRUNCATED AT 400 WORDS)

Archaea↗
PubMed1976

[Reaction of peripheral veins and arteries following administration of beta-active agents. Studies on isoproterenol, propranolol, and practolol].

The local effect on veins and arteries of isoprenaline, propranolol and practolol was investigated in the human after intra-arterial application at the forearm. The injection of isoprenaline was followed by a dilatation of the arteries and veins. This effect was inhibited by propranolol, but not by practolol. The results demonstrate, that the peripheral vasoactive beta-stimulatory effect is mediated by so-called beta2-receptors, which were not influenced by a selective beta1-blocking agent like practolol. The results were discussed in respect to their clinical relevance.

Adult↗