THEMES AND VARIATIONS

Themes and variations on ubiquitylation.

Ubiquitylation--the conjugation of proteins with a small protein called ubiquitin--touches upon all aspects of eukaryotic biology, and its defective regulation is manifest in diseases that range from developmental abnormalities and autoimmunity to neurodegenerative diseases and cancer. A few years ago, we could only have dreamt of the complex arsenal of enzymes dedicated to ubiquitylation. Why ...

Themes and Variations in Complex Systems

Variations on themes of Kostant

Let g be a complex semisimple Lie algebra, and let G be a complex semisimple group with trivial center whose root system is dual to that of g. We establish a graded algebra isomorphism H q (Xλ,C) ∼= Sg e/Iλ, where Xλ is an arbitrary spherical Schubert variety in the loop Grassmannian for G, and Iλ is an appropriate ideal in the symmetric algebra of g, the centralizer of a principal nilpotent in...

Themes and Variations in Validity Theory

s most of the readers of this A journal know, the 1985 Standards for Educational and Psychological Testing (AERA, MA, & NCME, 1985) is under revision. Deciding whether and how to revise the characterization of validity is probably the most significant issue facing the authors of the revised Standards. There is a substantial disjunction between the way validity is characterized in the 1985 stand...

Mechanisms of cell competition: Themes and variations

Cell competition is the short-range elimination of slow-dividing cells through apoptosis when confronted with a faster growing population. It is based on the comparison of relative cell fitness between neighboring cells and is a striking example of tissue adaptability that could play a central role in developmental error correction and cancer progression in both Drosophila melanogaster and mamm...