Q beta amplification.

We examined the expression of the trk protooncogene in a series of 82 neuroblastomas to determine its relationship to N-myc amplification and expression, disease stage, patient age, and survival. We found that virtually all stage I, II, and IV-S patients had moderate to high levels of trk expression, whereas most advanced stage neuroblastomas had low or absent levels. All but one tumor with N-myc amplification had low or absent trk expression, and the one exception was regressing at the time it was resected. Conversely, all neuroblastomas identified by mass screening had moderate to high expression of trk, and all these patients are surviving. Thus, trk expression was associated with an absence of N-myc amplification, lower disease stage, lower patient age, and favorable outcome. Tumors with high trk expression may be more likely to differentiate, regress spontaneously, or respond well to therapy.

Gene Amplification↗

PubMed1992

Regulation of fitness in yeast overexpressing glycolytic enzymes: parameters of growth and viability.

Current models predict that large increases over wild-type in the activity of one enzyme will not alter an organism's fitness. This prediction is tested in Saccharomyces cerevisiae through the use of a high copy plasmid that bears one of the following: hexokinase B (HEXB), phosphoglucose isomerase (PGI), phosphofructokinase (PFKA and PFKB), or pyruvate kinase (PYK). Transformants containing these plasmids demonstrate a four to ten-fold increase in enzyme specific activity over either the parent strain or transformants containing the plasmid alone. Haploid and diploid transformants derived from independent backgrounds were grown on both fermentable and non-fermentable carbon sources and evaluated for several components of fitness. These include growth rate under non-limiting conditions, maximum stationary phase density, and viability in extended batch culture. Cell viability is not affected by overproduction of these enzymes. Growth rate and stationary phase density do not differ significantly among strains that overexpress HEXB, PGI or contain the vector alone. PFKA, B transformants show reduced growth rate on glucose in one background only. For these loci the current model is confirmed. By contrast, when grown on glucose, yeast overexpressing PYK demonstrate reduced growth rate and increased stationary phase density in both backgrounds. These effects are abolished in cells containing plasmids with a Tn5 disrupted copy of the PYK gene. Our results are consistent with reports that the PYK locus may exert control over the yeast cell cycle and suggest that it will be challenging to model relations between fitness and activity for multifunctional proteins.

Gene Amplification↗