PubMed Health⌕ Search

Biomedical subjects

N C Nielsen

Publications and source records attributed to N C Nielsen.

At least 19 recordsLinked to original sources
PubMed1992

A simple and efficient method for the oligodeoxyribonucleotide-directed mutagenesis of double-stranded plasmid DNA.

A method for the oligodeoxyribonucleotide-directed mutagenesis of double-stranded DNA without the necessity for phenotypic selection is described. Plasmids denatured with alkali and purified by adsorption to and elution from nitrocellulose have single-stranded regions where primers can hybridize and serve as templates for a T7 DNA polymerase-catalyzed synthesis of complementary mutant DNA strands. When this procedure was carried out such that the original nonmutant strand contained uracil [method of Kunkel, Proc. Natl. Acad. Sci. USA 82(1985)488-492], mutation frequencies of between 30% and 40% were obtained. The technique has been used to generate mutant genes in plasmids of a wide variety of sizes. The largest plasmid manipulated and successfully mutagenized was 22 kb. The method is rapid and efficient and is not dependent upon either f1 phage vectors or the presence of restriction sites in the vicinity of the sequence targeted for mutation.

Base Sequence↗
PubMed1992

A protease responsible for post-translational cleavage of a conserved Asn-Gly linkage in glycinin, the major seed storage protein of soybean.

The assembly of 11S globulin seed storage proteins in plants is regulated in part by the activity of a protease that cleaves between asparagine and glycine residues. Post-translational cleavage of subunit precursors into acidic and basic polypeptides is associated with the ability of subunits in trimers to aggregate into hexamers in vitro. An activity is present in extracts from immature soybean seeds that specifically cleaves immature 11S seed storage proteins of soybean and Vicia faba into the polypeptides of the mature proteins. Sequence microanalysis has been used to demonstrate that proglycinin and prolegumin are cut at the legitimate site when proteins synthesized in vitro are used as substrates. A single amino acid change in the cleavage site renders the substrate uncleavable. The protease responsible for this activity also hydrolyzes a synthetic octapeptide whose sequence reproduces four amino acids on either side of the glycinin subunit G4 cleavage site. This assay permitted the purification and characterization of the protease. It is a glycosylated enzyme with an acidic pH optimum and a molecular mass of about 45 kDa in solution.

Amino Acid Sequence↗
PubMed1992

Synthesis and assembly of soybean beta-conglycinin in vitro.

The construction of SP6-derived expression plasmids that encode normal and modified beta-conglycinin subunits is described. With the exception of an additional methionine at their NH2-terminal ends and the lack of glycans, the normal subunits synthesized at the direction of these plasmids corresponded to mature alpha and beta subunits isolated from soybean seeds. The subunits assembled into trimers in vitro that were equivalent in size to those formed in vivo. This result shows that the glycans are not required either for protein folding or oligomer assembly. Subunits produced from other plasmids, which had modifications in a highly conserved hydrophobic region in the COOH-terminal end of the subunits, either did not assemble or assembled at an extremely low rate compared to unmodified subunits. Structural changes at the more hydrophilic NH2-terminal end had mixed effects. Several subunits modified in this region assembled into trimers at rates that were either equal or greater than those for normal alpha subunits. Others assembled less completely than the normal subunits. Our results indicate that the in vitro synthesis and assembly assay will be useful in evaluating structure-function relationships in modified beta-conglycinin subunits. The results also show that structural changes at the NH2-terminal end of the subunits are tolerated to a greater extent than modifications in the hydrophobic conserved region in the COOH-terminal half of the subunits, and this information will be useful in efforts to improve soybean quality.

Amino Acid Sequence↗
PubMed1991

Survival of chlamydiae in human semen prepared for artificial insemination by donor.

Semen specimens from 21 men with urethral infection with Chlamydia trachomatis were tested for the presence of the organism before and after cryopreservation for 3 weeks of storage at -196 degrees C. Five specimens were chlamydia-positive before preservation and four of them were still positive after storage when examined by enzyme immunoassay (Chlamydiazyme). When examined by cell culture, four proved chlamydia- positive before storage and two afterwards. The results indicate that testing for C. trachomatis has to be performed from the urethra of all donors of semen used for artificial insemination before the inoculation takes place.

Chlamydia Infections↗
PubMed1990

A randomized study of sequential versus alternating combination chemotherapy in advanced ovarian carcinoma.

The concept of using either alternating or sequential combination chemotherapy with non-cross-resistant combinations was tested in a randomized trial including 301 previously untreated patients with advanced epithelial ovarian carcinoma. The sequential schedule consisted of CAF (cyclophosphamide, doxorubicin, 5-fluorouracil) followed by PH (cisplatin, hexamethylmelamine) in nonresponders, CAF- greater than PH (n = 157), and the alternating regimen consisted of CAF/PH (n = 144). With a median observation time of 54 months, no statistically significant differences were found between the pathologically complete response (PCR) rates of 17% and 16%, respectively, nor were there any statistical differences in median disease-free survival for PCR patients (CAF- greater than PH 34+ months and CAF/PH 26+ months), in overall survival (28 and 24 months, respectively), or in time to treatment failure (10 and 11 months). The overall estimated cure rate was 13%. An equal degree of myelosuppression was seen with the two regimens, whereas neuro- and nephrotoxicity were more pronounced when PH was given sequentially to CAF than with the alternating schedule. We conclude that the sequential and the alternated use of doxorubicin- and platinum-based regimens yield equivalent results and that other approaches should be investigated to improve treatment effects.

Adult↗
PubMed1990

Effect of structural modifications on the assembly of a glycinin subunit.

A Gy4 glycinin cDNA was modified and used to produce structurally altered 11S storage protein subunits. We evaluated these modified subunits for their ability to assemble into oligomers. Alterations made in the acidic polypeptide changed the subunit solubility characteristics but did not eliminate assembly. Modifications in the basic polypeptide usually eliminated assembly of subunits into trimers. A region exhibiting high natural variability located at the COOH terminus of the acidic polypeptide that we have designated the hypervariable region was also studied. Extensive deletions and insertions were tolerated in the hypervariable region without perturbing subunit assembly. Some of the insertions significantly increased the methionine content in the Gy4 glycinin subunit. Together, our results indicated that the structure of the basic polypeptide was more critical for assembly of trimers than that of the acidic polypeptide, an observation that implies that the basic polypeptides direct trimer formation. The assembly assays described here will be useful in efforts to improve seed quality. Using them, the effects of modifications to the storage protein subunits can be rapidly evaluated before introducing the mutated genes into plants.

Base Sequence↗
PubMed1989

Characterization of the glycinin gene family in soybean.

We characterized the structure, organization, and expression of genes that encode the soybean glycinins, a family of storage proteins synthesized exclusively in seeds during embryogenesis. Five genes encode the predominant glycinin subunits found in soybeans, and they have each been cloned, sequenced, and compared. The five genes have diverged into two subfamilies that are designated as Group-I and Group-II glycinin genes. Each glycinin gene contains four exons and three introns like genes that encode related proteins in other legumes. Two other genes have been identified and designated as "glycinin-related" because they hybridize weakly with the five glycinin genes. Although not yet characterized, glycinin-related genes could encode other glycinin subunit families whose members accumulate in minor amounts in seeds. The three Group-I glycinin genes are organized into two chromosomal domains, each about 45 kilobase pairs in length. The two domains have a high degree of homology, and contain at least five genes each that are expressed either in embryos or in mature plant leaves. Gel blot studies with embryo mRNA, as well as transcription studies with 32P-RNA synthesized in vitro from purified embryo nuclei, indicate that glycinin and glycinin-related genes become transcriptionally activated in a coordinated fashion early in embryogenesis, and are repressed coordinately late in seed development. In addition to transcriptional control processes, posttranscriptional events also are involved in regulating glycinin and glycinin-related mRNA levels during embryogenesis.

Amino Acid Sequence↗
PubMed1989

Molecular characterization of an aberrant allele for the Gy3 glycinin gene: a chromosomal rearrangement.

The soybean variety Forrest contains an aberrant allele for the Gy3 glycinin gene. The aberrant allele is designated gy3 because mRNA for the G3 glycinin subunit is reduced to below detectable amounts in the seed. Molecular and genetic characterization of gy3 show it to be associated with a chromosomal rearrangement that causes the 5' halves and 3' halves of the gene to become separated from one another in the genome. An inversion is the simplest structural model that accounts for the genetic and molecular features of the chromosomal rearrangement involving gy3, although more complex models that involve reciprocal translocations are also consistent with the data.

Alleles↗
PubMed1989

Role of posttranslational cleavage in glycinin assembly.

Glycinin, like other 11S seed storage proteins, undergoes a complex series of posttranslational events between the time proglycinin precursors are synthesized in endoplasmic reticulum and the mature glycinin subunits are deposited in vacuolar protein bodies. According to the current understanding of this process, proglycinin subunits aggregate into trimers in endoplasmic reticulum, and then the trimers move to the vacuolar protein bodies where a protease cleaves them into acidic and basic polypeptide chains. Stable glycinin hexamers, rather than trimers, are isolated from mature seeds. We used a re-assembly assay in this study to demonstrate that proteolytic cleavage of the proglycinin subunits is required for in vitro assembly of glycinin oligomers beyond the trimer stage. The possibility that the cleavage is a regulatory step and that it triggers the deposition of 11S seed storage proteins as insoluble aggregates in vivo is considered.

Base Sequence↗
PubMed1989

Relationship among selected Leptospira interrogans serogroups as determined by nucleic acid hybridization.

Leptospiral DNAs from a variety of Leptospira interrogans serogroups of veterinary significance, as well as a nonpathogenic leptospira, were compared by Southern blot hybridization of EcoRI-digested genomic DNA. The serogroups examined could be assigned to one of three groups on the basis of the degree of cross-hybridization between genomic DNAs. Only a few restriction fragments hybridized between the three groups, and most of these were shown to contain ribosomal DNA. The restriction fragment length polymorphism observed among the intergroup hybridizations allowed differentiation among serogroups and, in some cases, serovars. Under the hybridization conditions used, no hybridization was observed between leptospiral DNA and Leptonema, Escherichia coli, or porcine DNA.

Animals↗
PubMed1989

Etiologic studies on late-term swine abortions.

One hundred thirty-eight swine abortions were studied in detail in an effort to identify an etiologic agent. A viral agent was implicated in 7 cases. Bacteria were isolated in less than half of the examined cases: however, in 61% of the cases, motile, filamentous organisms were observed in tissues and fluids. Although swine sera from farms experiencing reproductive problems had a high reactor rate to Leptospira bratislava antigen, electron microscopy of the observed organism revealed a wall-free prokaryote morphologically typical of the class Mollicutes.

Abortion, Veterinary↗
PubMed1989

Intestinal obstruction in patients with advanced carcinoma of the ovaries treated with combination chemotherapy.

An analysis of incidence, risk factors and treatment results of intestinal obstruction caused by carcinoma of the ovaries was performed in 310 consecutive patients with carcinoma of the ovaries, The International Federation of Gynecology and Obstetrics stage IIB to IV, treated with combination chemotherapy. With a median observation time of 46 months, the incidence was 14 per cent and the cumulated risk was estimated to be 26 per cent at five years after treatment was begun. Risk factors were stages IIIB and IV, residual primary tumor size greater than 2 centimeters and presence of intestinal carcinomatosis at primary laparotomy. There was no difference in the survival time between 16 conservatively treated patients and 25 surgically treated patients (a median of 30 and 68 days, respectively, p greater than 0.30). The complication risk of surgical treatment was high (64 per cent), and surgical benefit--defined as survival greater than 60 days with total palliation of intestinal symptoms--was achieved in only 32 per cent.

Adult↗
PubMed1985

Characterization of the subunits of beta-conglycinin.

Four subunits of beta-conglycinin were purified from soybean cultivar CX 635-1-1-1, and were designated alpha, alpha', beta, and beta' in accordance with nomenclature proposed by Thanh and Shibasaki [(1977) Biochim. Biophys. Acta 490, 370-384]. Of these subunits, beta' has not previously been reported or characterized. Consistent with the low levels of methionine in these proteins, cyanogen bromide cleavage of alpha', alpha, and beta' subunits produced only a few fragments. The beta subunit contains no methionine and was not cleaved by cyanogen bromide. The NH2-terminal amino acid sequences of the alpha and alpha' subunits are homologous, and each has valine at its amino terminus. The beta subunit has a very different NH2-terminal sequence from those of the alpha and alpha' subunits, and has leucine at its amino terminus. The NH2-terminal sequence of the beta' subunit could not be determined, as it appeared to be blocked to Edman degradation. Although alpha and alpha' subunits have similar NH2-terminal sequences, they differ in the number of methionine residues and so yielded different numbers of cyanogen bromide fragments. Two cyanogen bromide fragments (CB-1 and CB-2) were purified from the alpha subunit. CB-1 originated from the NH2-terminal end of the subunit. The amino acid sequence of CB-2 was identical to that predicted from the nucleotide sequence of cDNA clone pB36. The insert in pB36 encoded 216 amino acids from the COOH-terminal end of the alpha subunit and contained a 138-bp trailer sequence which was followed by a poly-(A) tail. Maps showing the relative positions of methionine residues and carbohydrate moieties in the alpha and alpha' subunits were drawn, based on primary sequence data, and the size and carbohydrate content of the CNBr fragments derived from the subunits.

Amino Acid Sequence↗
PubMed1985

Isolation of a cDNA clone for pea (Pisum sativum) seed lipoxygenase.

A lipoxygenase cDNA clone, pCD45, was identified in a Pisum sativum L. (pea) seed mRNA cDNA library by hybrid-release/translation followed by immunoprecipitation with antiserum raised against lipoxygenase from Glycine max L. (soya bean). pCD45 hybrid-selected an mRNA encoding the larger of the two polypeptides of Mr approximately 95 000 that were immunoprecipitated from cell-free translation products of pea seed poly(A)-containing RNA by the G. max anti-lipoxygenase. 'Northern'-blot analysis showed the mRNA that hybridized to pCD45 to be approximately 3000 nucleotides in length. Three to five copies of the lipoxygenase gene corresponding to pCD45 were estimated to be present per haploid Pisum genome; hybridization of the cDNA insert from pCD45 to G. max DNA was also detected.

Centrifugation, Density Gradient↗