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Biomedical subjects

M A Cochran

Publications and source records attributed to M A Cochran.

At least 37 records · Page 2Linked to original sources
PubMed1985

Eukaryotic transient expression system dependent on transcription factors and regulatory DNA sequences of vaccinia virus.

A transient expression system in which chimeric genes are expressed in cells infected with vaccinia virus was developed. Recombinant plasmids containing the promoter regions of vaccinia virus genes ligated to the coding segment of the prokaryotic chloramphenicol acetyltransferase (CAT) gene were constructed. When the plasmids were introduced into vaccinia virus-infected cells by transfection, the chimeric gene was expressed and significant levels of CAT accumulated. CAT activity was not detected when the same recombinant plasmid was introduced into uninfected cells, nor was activity detected when the vaccinia virus promoter was absent from the plasmid or was replaced by simian virus 40 or Rous sarcoma virus promoters. This specificity indicated that expression is dependent on a cis-acting vaccinia virus promoter region within the recombinant plasmid and diffusible trans-acting transcription factors produced during virus infection. The lack of effect of a simian virus 40 enhancer element inserted upstream of the vaccinia virus promoter region also distinguished this system from systems dependent on RNA polymerase II. Although replication of the recombinant plasmid could not be detected in either uninfected or vaccinia virus-infected cells, an inhibitor of DNA synthesis significantly reduced CAT expression. This result, as well as the kinetics of CAT synthesis, suggests that replication of viral DNA templates can enhance transcription of chimeric genes in recombinant plasmids.

Acetyltransferases↗
PubMed1985

In vitro mutagenesis of the promoter region for a vaccinia virus gene: evidence for tandem early and late regulatory signals.

A vaccinia virus gene that is expressed throughout the reproductive cycle was found to have two sets of RNA start sites approximately 55 nucleotides apart. The site nearest to the coding segment is used early in infection and the one further upstream is used after DNA replication. A series of 5' to 3' deletions were made in the promoter region, and the truncated DNA segments were then ligated to the coding portion of the procaryotic chloramphenicol acetyltransferase gene to measure expression. The effects of these mutations on chloramphenicol acetyltransferase synthesis were determined in a vaccinia virus helper-dependent transient expression system and by forming infectious vaccinia virus recombinants that contain the chimeric genes. Deletions extending up to 31 nucleotides before the late RNA start site had no effect on either early or late expression. Removal of an additional 15 nucleotides produced a dramatic decrease in late expression but had no effect on early expression. The latter was not diminished until the deletion was extended from 31 to 24 nucleotides before the early RNA start site. These results were confirmed by transcriptional analyses. We concluded that this vaccinia virus gene has two promoters and that the regulatory signals for each are located within 31 nucleotides of their sites of transcription.

Base Sequence↗
PubMed1983

Location of Homologous DNA Sequences Interspersed at Five Regions in the Baculovirus AcMNPV Genome.

An examination of Autographa californica nuclear polyhedrosis virus DNA revealed the presence of five interspersed regions, rich in EcoRI restriction sites, which shared homologous sequences. These homologous regions (hr), designated hr(1) to hr(5), occur at or near the following EcoRI fragment junctions: hr(1)EcoRI-B-EcoRI-I (0.0 map units); hr(2), EcoRI-A-EcoRI-J (19.8 map units); hr(3), EcoRI-C-EcoRI-G (52.9 map units); hr(4), EcoRI-Q-EcoRI-L (69.8 map units); and hr(5), EcoRI-S-EcoRI-X (88.0 map units). Four of these regions were identified, by cross-blot hybridization of HindIII-restricted A. californica nuclear polyhedrosis virus DNA, to be within the HindIII-A/B, -F, -L, and -Q fragments. The location of these regions and the identification of a fifth homologous region were confirmed, and their characterization was facilitated, by using two plasmids with HindIII-L or -Q fragment insertions, which contained the homologous regions hr(2) and hr(5), respectively. The sizes of the homologous regions were about 800 base pairs for hr(2), 500 base pairs for hr(5), and less than 500 base pairs for hr(1), hr(3), and hr(4). A set of small EcoRI fragments (EcoRI minifragments) which ranged in size from 225 to 73 base pairs were detected in A. californica nuclear polyhedrosis virus DNA and HindIII-L and -Q fragments by polyacrylamide gel analysis. Some of the minifragments in viral DNA were present in extramolar amounts and corresponded in size to some of the minifragments present in HindIII-L and -Q. Clones of some of the EcoRI minifragments were used as probes in hybridizations to digests of viral DNA and of HindIII-L and -Q. The hybridization data, obtained under various levels of stringency, suggested that there was a degree of mismatching between the sequences which were responsible for the homology.

Journal Article↗
PubMed1982

Molecular Cloning and Physical Mapping of Restriction Endonuclease Fragments of Autographa californica Nuclear Polyhedrosis Virus DNA.

A restriction fragment library containing Autographa californica nuclear polyhedrosis virus (AcNPV) DNA was constructed by using the pBR322 plasmid as a vector. The library, which is representative of more than 95% of the viral genome, consists of 2 of the 7 BamHI fragments, 12 of the 24 HindIII fragments, and 23 of the 24 EcoRI fragments. The cloned fragments were characterized and used to generate physical maps of the genome by hybridizing nick-translated recombinant plasmid to Southern blots of AcNPV DNA digested with SmaI, BamHI, XhoI, PstI, HindIII, and EcoRI restriction endonucleases. This information was used to define our strain of AcNPV (HR3) with respect to other strains for which physical maps have been previously published. The hybridization data also indicate that reiteration of DNA sequences occurs at the HindIII-L and -Q regions of the genome.

Journal Article↗
PubMedDate not supplied

Regarding dinosaurs.

Explore the source record for details and available documents.

Dental Care↗
PubMedDate not supplied

Microleakage of posterior packable resin composites with and without flowable liners.

The use of flowable composites as liners in Class II packable composites has been suggested by some manufacturers. However, the contributions of this technique are unproven. This study evaluated marginal microleakage in Class II packable composite restorations with and without the use of a flowable composite liner. A conventional microhybrid composite was used as a control. Microleakage at occlusal and gingival margins of Class II cavities was evaluated using 45Ca and autoradiographs. Fifty non-carious, restoration-free human molar teeth were used. Separate mesio-occlusal and disto-occlusal Class II cavity preparations were made in each tooth. Gingival margins of all cavities were placed 1 mm apical to the cementoenamel junction (CEJ). Four Packable composites (Alert, Surefil, Pyramid and Solitaire) and one conventional microhybrid composite (Renew) with their respective manufacturer's bonding agents were used to restore the cavities. One side of each tooth was restored with composite alone, while the other side was restored with the composite lined with that manufacturer's flowable liner. The restored teeth were thermally stressed and 45Ca was used to evaluate microleakage. Two independent evaluators scored leakage based on the autoradiographs. The results showed flowable composites helped reduce microleakage at gingival margins of Class II restorations (p < 0.05). Gingival margins had higher microleakage than occlusal margins (p < 0.05). Without flowable liners, three packable composites (Alert, Pyramid and Surefil) showed higher leakage (p < 0.05) than the microhybrid control. Only Solitaire packable composite without liner showed no significant difference in microleakage to the control (p > 0.05). Although the flowable liners help reduce microleakage, Alert and Pyramid packable composites with liners still showed higher leakage than the control (p < 0.05). Surefil and Solitaire packable composites with flowable liners showed no significant difference in microleakage (p > 0.05) to the control.

Analysis of Variance↗
PubMedDate not supplied

Degradation of bleaching gels in vivo as a function of tray design and carbamide peroxide concentration.

This study determined the degradation of nine bleaching agents with different concentrations after two hours in vivo following the manufacturers' recommendations. The nine carbamide peroxide products are 10%, 15% and 20% Opalescence, 10%, 15% and 22% Rembrandt and 10%, 16% and 22% Nite White Excel 2. Each subject wore the tray with the bleaching agent for two hours on three separate occasions. The amount of remaining carbamide peroxide was determined after each use. Evaluation of remaining amount of carbamide peroxide was calculated by the US Pharmacopeia method. The study showed that the total carbamide peroxide percent recovered was significantly higher for Opalescence products (47% to 54%) compared to Nite White (22% to 25%) and Rembrandt bleaching gels (15% to 16%). It concluded that this difference was mostly due to the use of facial reservoirs with Opalescence products, and also that whitening gel in trays with reservoirs and trays without reservoirs degraded at the same rate.

Adult↗
PubMedDate not supplied

A clinical evaluation of a bleaching agent used with and without reservoirs.

This in vivo study evaluated the variation of tray fabrication (trays constructed with or without reservoirs) on the degree of color change of teeth and sensitivities associated with using a 15% carbamide peroxide bleaching agent for two hours once daily for 14 days. Patients returned in one, two, three, six and 12 weeks. Color changes were evaluated by subjective shade matching, comparing clinical photographs and through measurements obtained using a color-measuring device. Subjects were asked to keep a daily record of any tooth and gingival sensitivity on the right and left side of their maxillary dental arch for three weeks. Colorimeter data showed that teeth lightened with agent with reservoirs were significantly lighter than teeth lightened with the same agent without reservoirs. However, the amount of lightening was below the threshold of visual differentiation. Shade guide and slide photography data showed no significant differences between teeth lightened with agent with reservoirs compared to teeth lightened with the same agent without reservoirs. In addition, no significant differences in tooth and gingival sensitivity were found between the tray side with reservoirs and those without reservoirs.

Adult↗