Search PubMed⌕ Search

Biomedical subjects

D H Hamer

Publications and source records attributed to D H Hamer.

90 records · Page 5Linked to original sources
PubMed1979

Splicing and the formation of stable RNA.

To determine whether RNA splicing plays an obligatory role in gene expression, we have constructed a series of SV40-transducing viruses carrying various combinations of splice junctions derived from the viral genome and a mouse globin gene. All of the viruses that retain at least one functional splice junction, derived from either the viral or the mouse genome, encode stable hybrid RNAs. In contrast, a virus from which all the splice junctions have been removed fails to produce any detectable stable RNA. These results suggest that splicing is a prerequisite for stable RNA formation.

Animals↗
PubMed1979

SV40 recombinants carrying rabbit beta-globin gene coding sequences.

We have constructed and propagated two SV40 recombinants in which different portions of the viral late gene region are replaced by a rabbit beta-globin coding sequence derived from a cloned cDNA (Maniatis et al., 1976). One of these recombinants, which retains the promoter, leader and intervening sequences for a viral late mRNA, directs the synthesis of a stable SV40-globin hybrid transcript. Using a sensitive radioimmunoassay, we have shown that this globin RNA is translated in infected monkey cells. A second recombinant, which retains the late region promoter but lacks the RNA splicing region, produces neither a stable globin transcript nor any detectable beta-globin. These experiments indicate that some sequence within a 500 bp SV40 segment, presumably the splicing region, is required for the accumulation of stable mRNA. They also demonstrate how hybrid transducing viruses can be used both to characterize viral regulatory sequences and to produce new gene products in cultured cells.

Animals↗
PubMed1979

SV40 recombinants carrying a functional RNA splice junction and polyadenylation site from the chromosomal mouse beta maj globin gene.

We have introduced a fragment of the chromosomal mouse beta major globin gene into SV40 and used the resultant hybrid virus to infect cultured monkey kidney cells. The mouse DNA fragment, which contains an intervening sequence and a poly(A) addition site, has been inserted in both possible orientations relative to the SV40 late region promoter. While the fragment is transcribed regardless of orientation, the RNA splice signal and poly(A) addition site are utilized only when the fragment is inserted in the "sense" orientation. Thus genomic mouse signals for both splicing and polyadenylation are recognized across species boundaries. Furthermore, since only an 18 bp segment was included on the 5' border of the intervening sequence, we can define a maximum length for this splice signal.

Animals↗
PubMed1978

Comparison of cloned mouse alpha- and beta-globin genes: conservation of intervening sequence locations and extragenic homology.

We have cloned and characterized a 9.7-kilobase EcoRI fragment of mouse DNA that contains an alpha-globin gene. The gene is encoded in at least three discontinous segments of DNA interrupted by two small intervening sequences that can be visualized as R-loop structures in the electron miscroscope. The size of the gene and its small intervening sequences fits well with the known size of the alpha-globin mRNA precursor, suggesting that these intervening sequences, like those of beta-globin, are transcribed. Partial sequence analysis indicates that the larger intervening sequence interrupts the alpha-globin gene at a site exactly corresponding to that interrupted by the larger intervening sequences in both the beta-globin major and minor genes. This observation suggests that these sequences were present when the alpha- and beta-globin genes diverged in early vertebrate evolution, more than 500 million years ago. Furthermore, though alpha and betamaj genes are encoded on different chromosomes, when their sequences are compared directly by visualization of heteroduplex structures, only one 150- to 200-base-pair segment of homology is recognized. These homologous sequences are located on the 3'-flanking segments of both genes, about 1.5 kilobases from each.

Animals↗
PubMed1978

Transduction of a bacterial gene into mammalian cells.

The transduction of an Escherichia coli gene into mammalian cells is described. A supressor tRNA gene was linked to a simian virus 40 (SV40) vector in vitro and the recombinant was used to transfect rat embryo cells and monkey kidney cells. The hybrid SV40 genome, SV40-su+ III, retained genetic information required for autonomous replication and cellular transformation and had a 1300-base-pair DNA segment in the late gene region (between the restriction endonuclease sits Hpa II at 0.735 and EcoRI at 0/1.0 on the SV40 genetic map) replaced by an 870-base-pair bacterial DNA segment containing the suppressor tRNA gene, su+ III (tRNATyrsu+III). The structure and fate of the SV40-su+III chimera were determined by DNA reassociation kinetic analysis and restriction enzyme cleavage of the total cellular DNA from transformed rat embryo cells and persistently infected monkey cells. Hybridization with radiolabeled probes specific for vector (SV40) or su+III DNA sequences revealed primarily nonintegrated or free hybrid genomes. In cloned lines of both cell types, the bacterial DNA segment was recovered intact, as judged by the length of the segment excised by restriction endonucleases and its ability to hybridize to the radiolabeled bacterial DNA probe and not to the SV40 probe.

Cell Line↗
PubMed1977

Interbacterial transfer of Escherichia coli--Drosophila melanogaster Recombinant plasmids.

Recombinants were constructed between various Escherichia coli plasmids and fragments of Drosophila melanogaster DNA. These recombinant plasmids are nonconjugative, but can be mobilized from one cell to another by conjugative sex factors. Of 47 recombinants studied, 46 were mobilized at approximately the same or slightly lower frequencies than the parental plasmids, whereas one was mobilized 1000 times less efficiently.

Conjugation, Genetic↗
PubMed1977

Molecular cloning.

Explore the source record for details and available documents.

Base Sequence↗
PubMed1976

Molecular cloning of DNA fragments produced by restriction endonucleases Sa1I and BamI.

The highly specific restriction endonucleases Sa1I and BamI produce DNA fragments with complementary, cohesive termini that can be covalently joined by DNA ligase. The Escherichia coli kanamycin resistance factor pML21 has one SalI site, at which DNA can be inserted without interfering with the expression of drug resistance or replication of the plasmid. A more convenient cloning vehicle can be made with the tetracycline resistance factor pSC101, since insertion of DNA either at its single site for Sa1I or at that for BamI inactivates plasmid-specified drug resistance but not replication. To take advantage of this insertional inactivation, pSC101 was joined to a Co1E1-ampicillin resistance plasmid having no Sa1I site, and to a Co1E1-kanamycin resistance plasmid having no BamI site. Chimeras formed with the resulting hybrid vehicles can be identified simply by replica plating. These three vehicles, which all replicate under relaxed control, have been used to clone and amplify Drosophila melanogaster DNA fragments.

Bacillus↗
PubMed1976

Characterization of talc and associated minerals.

The unequivocal identification of mineral impurities in talc requires definitive analytical techniques due to the very similar structure of many naturally occurring silicates and the small quantities of associated minerals frequently found. The instrumental methods and techniques extant for this purpose are reviewed. Light microscopy, x-ray diffractometry, and differential thermal analysis have been found to be particularly useful, complementary, and practical for both exploratory and routine determinations of mineral impurities in the talc matrix. When necessary, transmission electron microscopy is recommended for the analysis of mineral components present at sub-trace levels.

Chemical Phenomena↗
PubMed1975

Regular arrangement of restriction sites in Drosophila DNA.

When DNA of Drosophila melanogaster is digested to completion with Hemophilus aegyptius restriction endonuclease, the majority of the products are DNA segments whose lengths fits a random distribution with an average of 350 base pairs. However, some 10% of the DNA is recovered as various segments of discrete lengths, ranging from 30,000 to 365 base pairs. These segments arise from the regular spacing of the enzyme restriction sites in limited portions of the Drosophila genome. Three segments have been shown to originate from mitochondrial DNA, while all the others can be assigned to one or more isopycnic density classes of nuclear DNA. Five of the discrete fragments display modular lengths, each being an integral multiple of a 365 base pairs subunit. The relative frequencies of these multiple segments suggest that they are derived from DNA originally containing restriction sites every 365 base pairs, and that approximately 25% of these sites have been randomly inactivated.

Animals↗
PubMedDate not supplied

Age, temperature, and parasitaemia predict chloroquine treatment failure and anaemia in children with uncomplicated Plasmodium falciparum malaria.

The prevalence of chloroquine-resistant Plasmodium falciparum malaria has been increasing in sub-Saharan Africa and parts of South America over the last 2 decades, and has been associated with increased anaemia-associated morbidity and higher mortality rates. Prospectively collected clinical and parasitological data from a multicentre study of 788 children aged 6-59 months with uncomplicated P. falciparum malaria were analysed in order to identify risk factors for chloroquine treatment failure and to assess its impact on anaemia after therapy. The proportion of chloroquine treatment failures (combined early and late treatment failures) was higher in the central-eastern African countries (Tanzania, 53%; Uganda, 80%; Zambia, 57%) and Ecuador (54%) than in Ghana (36%). Using logistic regression, predictors of early treatment failure included younger age, higher baseline temperature, and greater levels of parasitaemia. We conclude that younger age, higher initial temperature, and higher baseline parasitaemia predict early treatment failure and a higher probability of worsening anaemia between admission and days 7 or 14 post-treatment.

Age Factors↗
PubMedDate not supplied

Competition for cellular factors that activate metallothionein gene transcription.

Metallothioneins (MTs), small cysteine-rich proteins, bind to and are inducible by heavy metals such as zinc, cadmium and copper. Recent gene-transfer and mutagenesis experiments have elucidated cis-acting DNA sequences involved in this form of regulation, but nothing is known about the trans-acting factors that interact with the control sequences or how such interactions influence the rate of transcription. We report here the detection of cellular factors involved in the cadmium induction of the mouse MT-1 gene by an in vivo competition assay. We show that at least one-class of these cellular factors acts by a positive regulatory mechanism depending on the same region of the 5' flanking DNA required for maximal transcription.

Animals↗