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Biomedical subjects

J Parker

Publications and source records attributed to J Parker.

At least 307 records · Page 17Linked to original sources
PubMed1980

Mistranslation in cells infected with the bacteriophage MS2: direct evidence of Lys for Asn substitution.

The coat protein of the bacteriophage MS2 was found to show an increased level of charge heterogeneity when synthesized in Escherichia coli starved for Asn or Lys. No such increase was found when the host was starved for Arg, His Ile or Pro. This is the pattern predicted by "two-out-of-three" codon misreading in the coat protein gene. In the case of Asn starvation, direct measurements of the relative incorporation of Lys demonstrate that the observed charge heterogeneity is the result of mistranslation. Asn starvation increased the error frequency in coat protein to over 0.3 mistake per asparagine codon. The small amount of charge heterogeneity seen in unstarved cells seems also to be the result of misreading Asn codons.

Asparagine↗
PubMed1980

Topography of the three late mRNA's of polyoma virus which encode the virion proteins.

The three cytoplasmic polyadenylated mRNA's which separately encode the three capsid proteins (VP1, VP2, and VP3) of polyoma virus were mapped on the viral genome by one- and two-dimensional gel electrophoreses of nuclease S1-resistant RNA-DNA hybrids. The mRNA's, which we designated mVP1, mVP2, and mVP3 to indicate the coding functions deduced from the cosedimentation of the RNAs and the messenger activities, comprise an overlapping set of 3'-coterminal molecules which also share a heterogeneous family of noncoding 5'-terminal regions (Flavell et al., Cell 16:357--371, 1979; Legon et al., Cell 16:373--388, 1979). The three species differ in the length of the 3' colinear coding region which is spliced to the 5' leader sequences. The common polyadenylated 3' end maps at map unit 25.3. The 5' ends of the colinear bodies of mVP1, mVP3, and mVP2 map at 48.5, 59.5, and 66.5 map units, respectively. An examination of the polyoma virus DNA sequence (Arrand et al., J. Virol. 33:606--618, 1980) in the vicinities of splicing sites approximated by the S1 gel mapping data for sequences common to the ends of known intervening sequences allowed prediction of the precise splice points in polyoma virus late mRNA's. In all three cases, the leader sequences are joined to the mRNA bodies at least 48 nucleotides before the translational initiation codon used in each particular messenger. The start signal which functions in each mRNA is the first AUG (or GUG) triplet after the splice junction.

Capsid↗
PubMed1979

Specialized lambda transducing bacteriophage which carries hisS, the structural gene for histidyl-transfer ribonucleic acid synthetase.

A number of specialized lambda transducing bacteriophages which carry the Escherichia coli gene guaB were isolated from E. coli. One of these bacteriophages, lambda cI857 Sam7 d guaB-2, also carries hisS, the structural gene for histidyl-transfer ribonucleic acid synthetase (EC 6.1.1.21). Histidyl-transfer ribonucleic acid synthetase activities in induced and uninduced lysogens carrying lambda d guaB-2 indicate that the phage carries the entire structural gene and that the gene is under the control of an E. coli promoter. These conclusions were confirmed by the in vivo production of a protein encoded by the phage which comigrates with authentic histidyl-transfer ribonucleic acid synthetase on two-dimensional polyacrylamide gels.

Amino Acyl-tRNA Synthetases↗
PubMed1979

Chimeric plasmids for cloning of deoxyribonucleic acid sequences in Saccharomyces cerevisiae.

Two sets of plasmids, each carrying a Saccharomyces cerevisiae gene and a portion or all of the yeast 2-micron circle linked to the Escherichia coli plasmid pBR322, have been constructed. One of these sets contains a BamHI fragment of S. cerevisiae deoxyribonucleic acid that includes the yeast his3 gene, whereas the other set contains a BamHI fragment of S. cerevisiae that includes the yeast leu2 gene. All plasmids transform S. cerevisiae and E. coli with a high frequency, possess unique restriction endonuclease sites, and are retrievable from both host organisms. Plasmids carrying the 2.4-megadalton EcoRI fragment of the 2-micron circle transform yeast with 2- to 10-fold greater frequency than those carrying the 1.5-megadalton EcoRI fragment of the 2-micron circle. Restriction endonuclease analysis of plasmics retrieved from S. cerevisiae transformed with plasmics carrying the 2.4-megadalton EcoRI fragment showed that in 13 of 96 cases the original plasmic has acquired an additional copy of the 2-mcron circle. These altered plasmids appear to have arisen by means of an interplasmid recombination event while in S. cerevisiae. A clone bank of S. cerevisiae genes based upon one of these composite plasmids has been constructed. By using this bank and selecting directly in S. cerevisiae, the ura3, tyr1, and met2 genes have been cloned.

Cloning, Molecular↗
PubMed1979

Use of 2-aminoacetophenone production in identification of Pseudomonas aeruginosa.

A grapelike odor is often of diagnostic importance in detecting the growth of Pseudomonas aeruginosa in culture and in burn wounds. The compound responsible for the odor has been identified as 2-aminoacetophenone by mass spectroscopy. Although the grape odor is sometimes difficult to detect in culture media, gas chromatographic, fluorometric, and colorimetric methods can be utilized to assay 2-aminoacetophenone production in a variety of media. Its synthesis occurs relatively early in the growth cycle. It has proved easy and convenient to detect 2-aminoacetophenone excretion by P. aeruginosa after 24 h of incubation on blood agar plates employing a fluorometric assay of ether extracts of the agar medium.

Acetophenones↗
PubMed1979

Supraorbital Doppler studies, carotid bruits, and arteriography in unilateral ocular or cerebral ischemic disorders.

In 122 patients with unilateral brain or ocular ischemia, supraorbital Doppler studies revealed evidence of obstruction in 44 of 51 common or internal carotid arteries having greater than 70 percent stenosis, and in only 4 of 23 arteries with 50 to 70 percent stenosis. Ipsilateral bruits were present in 52 of 74 carotid arteries with greater than 50 percent stenosis, and in 19 of 37 arteries with less than 50 percent stenosis. Only one false-positive Doppler result occurred, and only 15 false-positive midcervical bruits were present in 129 normal carotid arteries. Unfortunately, these studies do not decrease the need for radiopaque arteriography, since in 11 of 53 patients, a potentially operable, symptomatic, nonobstructive common or internal carotid artery lesion would not have been suspected by supraorbital Doppler testing and auscultation alone.

Angiography↗
PubMed1979

Primary grade children's memory for parts of speech.

Developmental differences in elementary school (kindergarten, first and second grade) children's free recall for parts of speech were investigated using sentences with normal and scrambled word order. The children were presented four sentences with normal syntax and four sentences with scrambled word order. There were significant effects of age, syntax, and rate of presentation; these replicated previous research. The unusual finding was that the kindergarten children, when presented with scrambled word strings, recalled more verbs than either the first or second grade children. It was hypothesized that this occurred because either the kindergarten children failed to detect the scrambled nature of syntaxless strings, or there is a change in the comprehension strategies which de-emphasizes the role of the verb.

Child↗
PubMed1979

Aortic aneurysm in Marfan's syndrome: changes in the ultrastructure and composition of collagen.

Aneurysmal aortic tissue and the mitral valve of a patient with Marfan's syndrome were examined. Biochemical analysis of the tissue showed a qualitative and quantitative defect in alpha 2 chain production of Type I collagen. On polyacrylamide gel electrophoresis of the aortic extract, two separate bands in the alpha 2 region and an increase of the alpha 1 to alpha 2 ratio were found. Examination by electron microscopy revealed elastic fibre degeneration, helical collagen fibres, and metabolically active modified smooth muscle cells. The formation of helical collagen fibres is attributed to a defect in the development of chains and cross-links of collagen precursors produced by the hypertrophic smooth muscle cells. Elastic fibre disintegration is believed to be due to a lack of support by Type I collagen fibres, which have decreased tensile strength. A scheme for the pathogenesis of aortic aneurysm and other connective tissue abnormalities in Marfan's syndrome is proposed as follows. Type I collagen fibres have decreased tensile strength because of a defect in the alpha 2 chain biosynthesis and decreased cross-linking. Over many years the wall of the ascending aorta is subjected to cyclic stresses and it dilates. Elastic fibres disintegrate. The attempt at repair by metabolically activated modified smooth muscle cells is abortive, and rupture is likely to occur.

Adult↗
PubMed1978

Hyaline cartilage changes in diastrophic dwarfism.

Hyaline cartilage of the talus of a diastrophic dwarf was studied by light and transmission electron microscopy before and after proteoglycan extraction or digestion, glycogen digestion, and enzyme marking. The nuclei of the chondrocytes were as a rule large and round and the cytoplasm contained large vacuoles. Best's carmine stained the cytoplasm of most cells red; after diastase digestion the cytoplasm remained unstained. This suggested that the cells contained glycogen. This observation was complimented by the ultrastructural demonstration of large amounts of glycogen. Cell scars were frequent. The shape and state of activity of the cells as well as the development of intracytoplasmic organelles showed great variability. The matrix showed many areas of degeneration and a general dearth of sulphated acid mucopolysaccharides. A lacey pattern of unmasked collagen fibers was frequently seen. Collagen fibers showed a great variability in diameter and often appeared frayed when examined by electron microscopy. These observations suggest an enzymatic deficiency in chondrocyte mucopolysaccharide and glucose metabolism. The techniques we used when added to biochemical studies should prove useful in the investigation of human dwarfism.

Cartilage↗
PubMed1978

Stuttering: high-level mistranslation in animal and bacterial cells.

In both bacterial and mammalian cells, extreme starvation for certain amino acids resulted in translational errors that could be easily detected by two-dimensional polyacrylamide gel electrophoresis. On two-dimensional gels, the faulty proteins were shown as a trail of spots with molecular weights similar to those of the authentic proteins but separated in the isoelectric focusing dimension, a phenomenon we call "stuttering." The direction of charge shift depended on the amino acid substituted and could be predicted from misreading of pyrimidines for purines at the third position of the codon. It is expected that this phenomenon will provide a rapid means of measuring the fidelity of the translational machinery from cell type to cell type.

Amino Acids↗