PubMed Health⌕ Search

Biomedical subjects

D Bamford

Publications and source records attributed to D Bamford.

13 recordsLinked to original sources
PubMed2000

Local average intensity-based method for identifying spherical particles in electron micrographs.

A method is presented that reliably detects spherical viruses from a wide variety of noisy low-contrast electron micrographs. Such detection is one of the first image analysis steps in the computer-aided reconstruction of three-dimensional density distribution models of viruses. Particle detection is based on the comparison of intensity in a circular area and in the surrounding ring followed by a number of tests to validate the potential particles. The only required input from the user in addition to the micrograph is an approximate radius of the particle. The method has been implemented as program ETHAN that has been tested for several different data sets. ETHAN has also successfully been used to detect DNA-less virus particles for an actual reconstruction.

DNA, Viral↗
PubMed1985

cDNA cloning of portions of the bacteriophage phi 6 genome.

Phage phi 6 has a genome consisting of three pieces of double-stranded RNA. Single-stranded RNA was prepared from phi 6 nucleocapsids by in vitro transcription with the phage RNA polymerase. These transcripts were polyadenylated and used as templates for the preparation of cDNA copies. The resulting DNA was cloned into the PstI restriction nuclease site of plasmid pBR322. Insert-bearing plasmids were annealed to phi 6 RNA to assign the inserts to their proper segments. In this way we identified inserts corresponding to the large, medium, and small segments. Two large overlapping inserts of the small segment constitute the complete complement of the segment as determined by the sequence analysis of the DNA. In vitro coupled transcription and translation showed that the small segment inserts were able to direct the synthesis of the four known genes in the small segment. Two overlapping inserts in the medium segment constitute the entire segment and were shown to direct the in vitro synthesis of two of the three known proteins of the medium segment. Several inserts bearing about one-third the complement of the large segment were also isolated, and one of these directed the synthesis of a peptide that resembles protein P1. Restriction endonuclease maps were prepared for the inserts, and by in vitro synthesis it was possible to refine the genetic map of phi 6. A chimeric plasmid was constructed that combines plasmids pUC8 and RSF1010. Inserts placed on this plasmid were transformed to Pseudomonas phaseolicola, the natural host of phage phi 6. It was possible to refine further the genetic map by complementation of nonsense mutants of phi 6 with the cDNA.

Acetyltransferases↗
PubMed1983

Identification of a protein bound to the termini of bacteriophage PRD1 DNA.

Lipid-containing bacteriophage PRD1 has a double-stranded DNA genome of about 14,500 nucleotide base pairs. The phage can infect Escherichia coli and Salmonella typhimurium as well as other gram-negative bacteria harboring an appropriate plasmid. [35S]methionine label is incorporated into the DNA band early in infection. The label remains associated with DNA through phenol extraction and boiling with sodium dodecyl sulfate. Nuclease treatment of the genome released a protein which migrated as an early phage-specific protein (P8). This protein is also necessary for phage DNA replication. By restriction enzyme analysis it was shown that protein was associated with the terminal restriction fragments. Extracts of infected cells catalyzed the labeling of protein P8 with [alpha-32P]dGTP.

Bacteriophages↗
PubMed1982

Isolation of nonsense mutants of lipid-containing bacteriophage PRD1.

We isolated nonsense mutants of bacteriophage PRD1, a lipid-containing polyhedral virus capable of infecting many genera of gram-negative bacteria. These mutants were grouped into 19 classes on the basis of genetic complementation and sodium dodecyl sulfate-polyacrylamide gel electrophoretic analysis. PRD1 infection led to the synthesis of at least 25 viral proteins, 17 of which were components of mature virions. The synthesis of proteins fell into the following three classes: very early, middle early, and late. Two of the very early proteins, P1 and P8, had an effect on DNA synthesis, host protein synthesis shutoff, and the turning on of middle and late protein synthesis. Another very early protein, P12, was involved in the shutoff of early protein synthesis. Two genes were identified as affecting lysis of the host. One appeared to be a lysin, whereas the other was an accessory lytic factor.

Genetic Complementation Test↗
PubMed1982

Assembly of bacteriophage PRD1: particle formation with wild-type and mutant viruses.

Bacteriophage PRD1 contains DNA, 17 proteins, and lipid. The assembly pathway involves the formation of empty particles that contain lipid and all of the proteins of mature virions, with the possible exception of one. The major and minor capsid proteins, P3 and P5, occur as soluble multimers before they appear in the empty particles. Nonsense mutants of PRD1 that involve structural proteins of the virion other than P3 form particles that are missing only the defective protein. Those mutants that are unable to form P3 do not form particles. Mutations in two other genes that code for nonstructural proteins (P10, which is membrane bound, and P17, which is soluble) result in the absence of particles. Protein P2 is necessary for adsorption to host cells. Protein P9 is necessary for particle filling with DNA, whereas P20 and P22 are necessary for stable DNA packaging. Electron micrographs of infected cells confirmed the gradient analysis of particle formation. No free vesicles were observed in mutants that could not form complete empty particles, indicating that there are no free intermediate particles before the empty virions.

Bacteriophages↗
PubMed1982

Structure of the lipid-containing bacteriophage PRD1: disruption of wild-type and nonsense mutant phage particles with guanidine hydrochloride.

The lipid-containing bacteriophage PRD1 was disrupted, and the subviral particles were studied. Guanidine treatment released two phage proteins (P3 and P5). These proteins form the polyhedral capsid. The remaining phage proteins were associated with the phage membrane vesicle. The vesicle was capable of forming a tubular structure. The isolated phage membrane vesicles aggregated readily. We found that aggregation and tube formation were associated with specific phage proteins (P11 and P18, respectively) by using protease treatment and an analysis of nonsense mutant phage particles. In addition, the possibility that free vesicles might be precursors to empty virions was studied.

Bacteriophages↗
PubMed1976

Mutangenicity and toxicity of amitrole. I. Drosophila tests.

Amitrole was highly toxic at early larval stages of Drosophila (LD50 is 40 ppm in medium). Toxicity of amitrole was also revealed by prolongation of development time even at 10 ppm. However, no mutagenic effects of amitrole were observed either in the sex chromosome non-disjunction test (females reared on medium containing amitrole at 10 ppm) or in the sex-linked recessive lethal test (males reared on medium containing amitrole at 10 ppm).

Amitrole↗
PubMed1976

Mutagenicity and toxicity of amitrole. II. Human lymphocyte culture tests.

Effects of amitrole (3-amino-1,2,4-triazole) on human leucocytes in culture were investigated. Amitrole interfered with lymphoblast transformation and inhibited cell growth in concentrations of 0.2% w/v and higher. Selected metaphases were examined for the presence of chromosome and chromatid aberrations. No clastogenic effects were observed.

Amitrole↗
PubMed1976

Mutagenicity and toxicity of amitrole. III. Microbial tests.

Amitrole (3-amino-1,2,4-triazole) inhibits bacterial growth both in Escherichia coli and Salmonella typhimurium at a concentration of 0.5% in minimal medium. Repression of growth already occurs at a concentration of 0.1% of amitrole in this medium. In complete medium the bacteria tolerate concentrations of amitrole as high as 1.7-2.4% before growth ceases. Mutagenicity was tested by differential growth comparisons on E. coli strains W 3110 thy pol A1, defective in DNA polymerase I, and its revertant pol A+. Known mutagens (MMS, NTG, mitomycin C) were used as positive controls. Analogous negative results were also obtained in a revertant test when several trp mutant strains of Salmonella were used.

Amitrole↗