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Biomedical subjects

A Christensen

Publications and source records attributed to A Christensen.

At least 73 records · Page 4Linked to original sources
PubMed1986

Translational regulation of expression of the bacteriophage T4 lysozyme gene.

The bacteriophage T4 lysozyme gene is transcribed at early and late times after infection of E. coli, but the early mRNA is not translated. DNA sequence analysis and mapping of the 5' ends of the lysozyme transcripts produced at different times after T4 infection show that the early mRNA is initiated some distance upstream from the gene. The early mRNA is not translated because of a stable secondary structure which blocks the translational initiation site. The stable RNA structure has been demonstrated by nuclease protection in vivo. After DNA replication begins, two late promoters are activated; the late transcripts are initiated at sites such that the secondary structure can not form, and translation of the late messages occurs.

Amino Acid Sequence↗
PubMed1986

Treatment of transsphincteric anal fistulas by the seton technique.

Twenty-one patients with high transsphincteric fistulas treated by the seton technique were re-examined after two to 14 years. None had recurrent fistulas, but 13 (62 percent) had some degree of continence disturbances. All patients with anal deformities had continence disorders.

Adult↗
PubMed1986

The effect of naloxone on the preoperative gastric volume and pH.

The effect of 4 mg oral naloxone on preoperative gastric volume and pH of gastric aspirate was studied in a double-blind, randomized study. Twenty patients received 10 ml of naloxone (4 mg) mixed with 10 ml of orange juice, and 20 patients received 10 ml of isotonic saline mixed with 10 ml of orange juice, 2 h before surgery. Gastric content was obtained immediately after intubation of the trachea. No significant difference in gastric volume and pH of gastric aspirate was found between the two groups. It is concluded that naloxone does not affect gastric emptying and gastric acid secretion to a degree great enough to protect against aspiration of gastric contents into the lungs.

Adult↗
PubMed1985

Alternative conformers of 5S ribosomal RNA and their biological relevance.

Different conformational states of Escherichia coli 5S ribosomal RNA that may participate in protein biosynthesis have been either detected experimentally or predicted on the basis of phylogenetic sequence comparisons. The A conformer exists in a high-salt form (AH) that binds ribosomal proteins and assembles into the 50S subunit and in a low-salt form (AL), of uncertain biological relevance, that binds at least one ribosomal protein and differs in tertiary structure from the AH form. Experimentally, the AH form has been investigated comprehensively and the AL form partially. There is also a B conformer that exhibits an altered secondary structure and does not assemble with ribosomal proteins. For this conformer exhibits an altered secondary structure and does not assemble with ribosomal proteins. For this conformer to be functionally active, it must be both discrete and universal among 5S RNAs. Here, we examine its structure by employing single and double strand specific ribonucleases and nucleotide-specific chemical reagents. We demonstrate that the B form exhibits a secondary structure only a part of which is both universal and conformationally homogeneous, and we conclude, therefore, that the whole B form cannot participate in protein biosynthesis. We note, however, that progressive structural changes occur during the transitions AH----AL----B and provide evidence that the structural alteration during the transition AH----AL may be universal, which reinforces the view that the AL form is of biological relevance.

Electrophoresis, Polyacrylamide Gel↗
PubMed1985

Does unpaired adenosine-66 from helix II of Escherichia coli 5S RNA bind to protein L18?

Adenosine-66 is unpaired within helix II of Escherichia coli 5S RNA and lies in the binding site of ribosomal protein L18. It has been proposed as a recognition site for protein L18. We have investigated further the structural importance of this nucleotide by deleting it. The 5S RNA gene of the rrnB operon of E. coli was subjected to primer-directed mutagenesis. To produce the deletion it was necessary to use simultaneously the mutagenic dodecamer dCGGCGCACGGCG and the universal M13 primer dCCCAGTCACGACGTT, and to employ forced annealing conditions. The mutated gene was expressed in an overproducing plasmid derived from pKK3535. Binding studies with protein L18 revealed that the protein bound much more weakly to the mutated 5S RNA. We consider the most likely explanation of this result is that L18 interacts with adenosine-66, and we present a tentative model for an interaction between the unpaired adenosine and the adjacent guanosine-67 of the RNA and glutamine-19 of the protein L18.

Adenosine↗
PubMed1984

Higher-order structure in the 3'-terminal domain VI of the 23 S ribosomal RNAs from Escherichia coli and Bacillus stearothermophilus.

An experimental approach was used to determine, and compare, the higher-order structure within domain VI of the 23 S ribosomal RNAs from Escherichia coli and Bacillus stearothermophilus. This domain, which encompasses approximately 300 nucleotides at the 3' end of the RNAs, consists of two large subdomains. The 5' subdomain has been conserved during evolution and appears to be functionally important for the binding of the EF-1 X GTP X aminoacyl-tRNA complex in eukaryotes. The 3' subdomain has diverged widely between eubacteria and eukaryotes, and has produced the 4.5 S RNA in the chloroplast ribosomes of flowering plants. The structure of domain VI within the eubacterial RNAs was probed with chemical reagents in order to establish the degree of stacking and/or accessibility of each adenosine, cytidine and guanosine residue; the double-helical segments were localized with the cobra venom ribonuclease from Naja naja oxiana, and the relatively unstructured and accessible sequences were detected with the single-strand-specific ribonucleases A, T1 and T2. The data enabled the three secondary structural models, proposed for the E. coli 23 S RNAs, to be examined critically and it was concluded that many of their structural features are correct. Various differences between the models were considered and evidence is provided for additional structuring in the RNA including the stacking of juxtaposed purines into double helices. The 5' subdomain constitutes a compact and resistant structure whereas the 3' subdomain is relatively accessible and contains most of the potential protein binding sites. Moreover, comparison of our results with the published results on 4.5 S RNA suggests that the latter forms essentially the same structure as the 3' subdomain, in contrast to earlier conclusions. A high level of structural conservation has occurred throughout the RNA domain during the evolution of the Gram negative and Gram positive bacteria although the thermophile was generally more stable at base-pairs adjacent to the terminal loops.

Alkylating Agents↗
PubMed1984

Patterns of alliances in nondistressed and multiproblem families.

The goal of this study was empirically to investigate differences between distressed and nondistressed families in the strength, patterning, and cross-situational consistency of alliances. Audiotapes were made of 12 distressed and 12 nondistressed families in two observational situations. The resultant interaction was then coded for family alliances by trained observers. Distressed families were characterized by low overall levels of alliance behavior, weakness in the marital alliance relative to other family alliances, and discrepancies in parental alliances with the target child. There were generally no differences between groups in the cross-situational variability of alliance strength or patterning. The results are discussed in relation to the predictions of structural models of family process.

Adolescent↗
PubMed1983

Higher order structure in the 3'-minor domain of small subunit ribosomal RNAs from a gram negative bacterium, a gram positive bacterium and a eukaryote.

An experimental approach was used to determine and compare the highest order structure within the 150 to 200 nucleotides at the 3'-ends of the RNAs from the small ribosomal subunits of Escherichia coli, Bacillus stearothermophilus and Saccharomyces cerevisiae. Chemical reagents were employed to establish the degree of stacking and/or accessibility of each adenosine, guanosine and cytidine. The double helices were probed with a cobra venom ribonuclease from Naja naja oxiana, and the relatively unstructured and accessible sequences were localized with the single strand-specific ribonucleases A, T1, T2 and S1. The data enabled the various minimal secondary structural models, proposed for the 3'-regions of the E. coli and S. cerevisiae RNAs, to be critically examined, and to demonstrate that the main common features of these models are correct. The results also reveal the presence and position of additional higher order structure in the renatured free RNA. It can be concluded that a high level of conservation of higher order structure has occurred during the evolution of the gram negative and gram positive eubacteria and the eukaryote in both the double helical regions and the "unstructured" regions. Several unusual structural features were detected. Multiple G X A pairings in two of the putative helices, which are compatible with phylogenetic sequence comparisons, are strongly supported by the occurrence of cobra venom ribonuclease cuts adjacent to, and in one case between, these pairings. Evidence is also provided for the stacking of an A X A pair within a double helix of the yeast RNA. Other special structural features include adenosines bulged out from double helices; such nucleotides, which are hyper-reactive, have been implicated in protein recognition in 5 S ribosomal RNA. The 3'-terminal regions of the RNAs are particularly important for the functioning of the ribosome. They are involved in mRNA, tRNA and ribosomal factor binding. The results reveal that while the functionally important RNA sequences tend to be conserved, they are not always accessible in the free RNA; the pyrimidine-rich "Shine and Dalgarno" sequence, for example, which is involved in mRNA recognition, occurs in a double helix in both eubacterial RNAs.

Base Sequence↗
PubMed1983

Children's perceptions of parental behaviors.

Children's perceptions of positive and negative parental behaviors were assessed using a newly-developed scale, the Parent Perception Inventory (PPI). Reliability and validity were examined across a sample of 75 children aged 5 to 13 using additional measures administered to the children and measures completed by their parents. The scale showed acceptable levels of internal consistency. No effects of children's age were apparent, but effects of the child's and parent's gender were found. Boys reported more positive parental behaviors, particularly for fathers, and children reported more negative (disciplinary) behaviors by mothers. PPI scores were predictably related to child's self-concept and behavior problems (convergent validity) and generally unrelated to measures of child's achievement (discriminant validity). As predicted by family systems theory, children from nondistressed families viewed their parents as behaving more similarly on the PPI than did children from distressed families.

Adolescent↗