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Biomedical subjects

P Shaw

Publications and source records attributed to P Shaw.

At least 163 records · Page 9Linked to original sources
PubMed1984

Caulobacter crescentus fatty acid-dependent cell cycle mutant.

A fatty acid auxotroph of Caulobacter crescentus, AE6001, which displays a strict requirement for unsaturated fatty acids to grow on glucose as the carbon source has been isolated. Starvation of AE6001 for unsaturated fatty acids resulted in a block in the cell cycle. Starved cultures accumulated at the predivisional cell stage after a round of DNA replication had been completed and after a flagellum had been assembled at the pole of the cell. Cell division and cell growth failed to occur probably because the mutant was unable to synthesize a membrane. An analysis of double mutants containing the fatB503 allele and other mutations in membrane biogenesis demonstrated that the cell cycle of AE6001 blocked at a homeostatic state. The addition of oleic acid to starved cultures permitted cell division and the initiation of a new round of DNA replication. The coincident block in both the initiation of DNA replication and membrane assembly, exhibited by starved cultures of this mutant, suggests that the fatB503 gene product may be involved in the coordination of these events.

Bacteria↗
PubMed1984

Genetic analysis and characterization of a Caulobacter crescentus mutant defective in membrane biogenesis.

A mutant of Caulobacter crescentus has been isolated which has an auxotrophic requirement for unsaturated fatty acids or biotin for growth on medium containing glucose as the carbon source. This mutant exhibits a pleiotropic phenotype which includes (i) the auxotrophic requirement, (ii) cell death in cultures attempting to grow on glucose in the absence of fatty acids or biotin, and (iii) a major change in the outer membrane protein composition before cell death. This genetic lesion did not appear to affect directly a fatty acid biosynthetic reaction because fatty acid and phospholipid syntheses were found to continue in the absence of supplement. Oleic acid repressed fatty acid biosynthesis and induced fatty acid degradation in the wild-type parent, AE5000 . The mutant strain, AE6000 , was altered in both of these regulatory functions. The AE6000 mutant also showed specific inhibition of the synthesis of outer membrane and flagellar proteins. Total phospholipid, DNA, RNA, and protein syntheses were unaffected. The multiple phenotypes of the AE6000 mutant were found to cosegregate and to map between hclA and lacA on the C. crescentus chromosome. The defect in this mutant appears to be associated with a regulatory function in membrane biogenesis and provides evidence for a direct coordination of membrane protein synthesis and lipid metabolism in C. crescentus.

Bacteria↗
PubMed1983

Methylation involved in chemotaxis is regulated during Caulobacter differentiation.

Caulobacter crescentus carries a flagellum and is motile only during a limited time in its cell cycle. We have asked if the biochemical machinery that mediates chemotaxis exists coincident with the cell's structural ability to respond to a chemotactic signal. We first demonstrated that one function of the chemotaxis machinery, the ability to methylate the carboxyl side chains of a specific set of membrane proteins (methyl-accepting chemotaxis proteins, MCPs), is present in C. crescentus. This conclusion is based on the observations that (i) methionine auxotrophs starved of methionine can swim only in the forward direction (comparable to smooth swimming in the enteric bacteria), (ii) a specific set of membrane proteins was found to be methylated in vivo and the incorporated [3H]methyl groups were alkali sensitive, (iii) this same set of membrane proteins incorporated methyl groups from S-adenosylmethionine in vitro, and (iv) out of a total of eight generally nonchemotactic mutants, two were found to swim only in a forward direction and one of these lacked methyltransferase activity. Analysis of in vivo and in vitro methylation in synchronized cultures showed that the methylation reaction is lost when the flagellated swarmer cell differentiates into a stalked cell. In vivo methylation reappeared coincident with the biogenesis of the flagellum just prior to cell division. In vitro reconstitution experiments with heterologous cell fractions from different cell types showed that swarmer cells contain methyltransferase and their membranes can be methylated. However, newly differentiated stalked cells lack methyltransferase activity and membranes from these cells cannot accept methyl groups. These results demonstrate that MCP methylation is confined to that portion of the cell cycle when flagella are present.

Bacteria↗
PubMed1982

Synthesis and utilization of fatty acids by wild-type and fatty acid auxotrophs of Caulobacter crescentus.

The fatty acid composition of the dimorphic bacterium Caulobacter crescentus was found to consist primarily of 16- and 18-carbon fatty acids, both saturated and monounsaturated, in agreement with the findings of Chow and Schmidt (J. Gen. Microbiol. 83:359-373, 1974). In addition, two minor but as yet unidentified fatty acids were detected. Chromatographic mobilities suggested that these fatty acids may be a cyclopropane and a branched-chain fatty acid. In addition, we demonstrated that the fatty acid composition of wild-type C. crescentus can be altered by growing the cells in medium supplemented with any one of a variety of unsaturated fatty acids. Linoleic acid, a diunsaturated fatty acid which is not synthesized by C. crescentus, was incorporated into phospholipids without apparent modification. In addition, we found that C. crescentus, like Escherichia coli, synthesizes vaccenic acid (18:1 delta 11,cis) rather than oleic acid (18:1 delta 9,cis). This result allowed us to deduce that the mechanism of fatty acid desaturation in C. crescentus is anaerobic, as it is in E. coli. Finally, we examined the fatty acid biosynthesis and composition of two unsaturated fatty acid auxotrophs of C. crescentus. Neither of these mutants resembled the E. coli unsaturated fatty acid auxotrophs, which have defined enzymatic lesions in fatty acid biosynthesis. Rather, the mutants appeared to have defects relating to the complex coordination of membrane biogenesis and cell cycle events in C. crescentus.

Bacteria↗
PubMed1981

Intravenous solutions in parenteral nutrition.

A review of the theoretical basis on which amino acid intravenous solutions are formulated leads to the conclusion that the first class protein model is not ideal for the very small premature infant. Comparison of the serum and urine amino acid levels in a controlled trial between intravenous feeding with "Vamin" and intragastric milk feeding, and further comparison of these values with the cord blood values of premature infants supports the conclusion that the first class protein model is not ideal. The balance studies also support the view that the urinary output of amino acids, as well as the serum levels, should be taken into account in determining the ideal amino acid input.

Amino Acids↗
PubMed1980

Drug trials: treatment of urinary tract infection with multiple-dose intramuscular administration of cephamandole.

Therapy with cephamandole (1.0 g, every eight hours) for five days was effective in eliminating cephamandole-sensitive microorganisms from the urinary tract. A 75% cure rate was achieved in a group of 20 patients, 45% of whom had abnormalities of the urinary tract. Local pain (despite addition of lignocaine) was sufficiently prolonged and severe to make multiple-dose intramuscular administration unacceptable. No other toxic effects were encountered.

Anti-Infective Agents, Urinary↗
PubMed1979

A comparison of three behaviour therapies in the treatment of social phobia.

This study examined the effects of desensitization, flooding and social skills training on social fears. The patients were 30 social phobics. All three treatments were associated with useful therapeutic gains during the period of treatment that were maintained over a six-month follow-up period. No differences were found between treatments.

Adult↗
PubMed1978

Reliability of the CPRS between the disciplines of psychiatry, general practice, nursing and psychology in depressed patients.

To test the reliability and robustness of the CPRS in use by different disciplines we obtained 49 pairs of ratings on depressed patients in England and Sweden during treatment. Each rater pair consisted of a psychiatrist trained as a rater plus either a psychologist, a general practitioner, or a nurse, who had not been trained as a rater. The 17 most commonly rated items in depressive illness showed good inter-rater reliability for all groups and demonstrated the robustness of the scale even in training sessions. The implications of this for future interdisciplinary research are discussed along with suggestions for the use of the CPRS for teaching purposes.

Depression↗
PubMed1977

Optimal allocation of cognitive resources to spatial locations.

From experiments showing that subjects differentially attend to parts of the visual field, psychologists have inferred a limitation on human visual information processing capacity. The model presented describes an optimal way to allocate a limited quantity of "cognitive resources," "attention" or "mental effort". For this model, the sense of optimality is maximizing the probability of finding a target. In an experiment to test the model, subjects searched for a single target letter in an otherwise blank field. Two probability distributions were used to select a target location for a trial, but only one distribution was used for a session. For both distributions, the fit of the model was quite good. It is suggested that the model provides a promising way to test the assumption limited visual processing capacity.

Adolescent↗