Biomedical subjects
Publications and source records attributed to G T Lee.
Leukemia is the major form of cancer in children in Britain and mirrors the percentage of children affected in the USA. This report outlines some of the medical aspects of leukemia and its treatment and gives a guide to the dentist, who may have the responsibility of dealing with leukemic children and their families.
Explore the source record for details and available documents.
Peptide production in senescent and presenescent human foreskin fibroblasts was measured using 2-dimensional polyacrylamide gel electrophoresis. This procedure permits the visualization of a cohort of the major peptides being produced. Among this cohort of over 500 peptides only two were found to differ in relative amount in that more was being produced in senescent cells. This difference was confirmed by measurements of the relative intensity of the peptide spot. This difference was senescent cell-specific and not due to the differences in rate of growth of senescent and non-senescent cells.
Patterns of newly synthesized proteins of Vero cells in different growth states were obtained using two-dimensional gel electrophoresis. The 240 most prevalent peptide spots were then compared. Cells in exponential growth and in the stationary phase were found to have patterns of peptide spots characteristic of their state of growth. The transition between these patterns is progressive, and the cells acquire a pattern characteristic of quiescent cells by the late exponential phase. These observations suggest that a series of modulations in gene expression occurs during the transition of growth states in animal cells that leads to the specific appearance or disappearance of certain cellular peptides.
Monkey fibroblasts maintained in culture regulate their levels of intracellular protein throughout the growth cycle by means of variations in the rate of protein biosynthesis. Cytoplasmic mRNA in stationary phase cells was compared to that in exponential phase cells. In stationary phase cells 56% of the cytoplasmic polyadenylated RNA was found in the 40--90S postpolysomal region of sucrose sedimentation gradients, while only 23% was found in this region in exponential phase cells. Analysis of electron micrographs of sectioned exponential and stationary phase cells revealed that this shift in polyadenylated RNA location is accompanied by a loss of polysome-like aggregates of ribosomes. Most if not all of this species of postpolysomal polyadenylated RNA is not being translated by single ribosomes since no detectable amounts of nascent peptide were present in this region. This nonpolysomal polyadenylated RNA is comparable in size to polysomal polyadenylated RNA. The length of the 3'-poly(A) tract was also comparable for these two species. The extent of capping of poly(A)-containing molecules was also comparable for these two species. The template activity of nonpolysomal RNA in a wheat germ extract was comparable to that of polysomal RNA. The peptides produced by these two preparations were of a similar large size. Furthermore, most of the nonpolysomal polyadenylated RNA of stationary phase cells was driven into polysomes in the presence of a low dose of cycloheximide. Therefore, we conclude that the untranslated mRNA that accumulates in stationary phase cells is structurally intact, is fully capable of being translated, and is not being translated due to the operation of a translational initiation block.
Protein synthesis and degradation were studied throughout a growth cycle of Vero cells. The rate of protein synthesis, measured as the rate of amino acid incorporation, reached a maximum at the mid-exponential phase and declined to 10-30% of the maximum in the stationary phase. The rate of protein degradation, measured as the release of radioactive amino acids from uniformly labelled cellular proteins, did not vary in the growth cycle. The amount of protein per cell, measured by an isotopic method, remained constant when normalized to account for the variation in the proportion of actively dividing cells in the cell population during the growth cycle. Cellular protein was determined using this method since it was found that the chemical determination of the amount of protein in the monolayer was not accurate during the early stage of the growth cycle. This was due to a significant amount of serum protein adsorbed to the cells. In this study we were able to show that, in Vero cells, protein synthetic activity is correlated with the rate of cell division, and variations in the rate of synthesis alone are sufficient to meet the changing requirements for cellular protein in a growth cycle.
Explore the source record for details and available documents.
The dental caries prevalence of adult Chinese immigrants in the Liverpool area is considerably lower than that of the native British. This is in contrast to Chinese children born in the U.K. who appear to have a higher prevalence compared to the same age group of British children.
Explore the source record for details and available documents.