Results, Old and New, in Computed Tomography

Introduction Computed tomography (CT) entails the reconstruction of a function f from line integrals of f . This mathematical problem is encountered in a growing number of diverse settings in medicine, science, and technology, ranging from the famous application in diagnostic radiology to recent research in quantum optics. As a consequence, many aspects of CT have been extensively studied and are now well understood, thus providing an interesting model case for the study of other inverse problems. Other aspects, notably three-dimensional reconstructions, still provide numerous open problems. The present article grew out of a series of tutorial talks given by the author at the IMA. In the spirit of such talks, it attempts to provide a brief introduction to the subject, highlight some aspects of general interest, sketch some recent developments, and point out references for further study. In practice only integrals over finitely many lines can b

Functional Contributions of Prefoldin to Gene Expression

Prefoldin is a co-chaperone that evolutionarily originates in archaea, is universally present in all eukaryotes and acts as a co-chaperone by facilitating the supply of unfolded or partially folded substrates to class II chaperonins. Eukaryotic prefoldin is known mainly for its functional relevance in the cytoplasmic folding of actin and tubulin monomers during cytoskeleton assembly. However, the role of prefoldin in chaperonin-mediated folding is not restricted to cytoskeleton components, but extends to both the assembly of other cytoplasmic complexes and the maintenance of functional proteins by avoiding protein aggregation and facilitating proteolytic degradation. Evolution has favoured the diversification of prefoldin subunits, and has allowed the so-called prefoldin-like complex, with specialised functions, to appear. Subunits of both canonical and prefoldin-like complexes have also been found in the nucleus of yeast and metazoan cells, where they have been functionally connected with different gene expression steps. Plant prefoldin has also been detected in the nucleus and is physically associated with a gene regulator. Here we summarise information available on the functional involvement of prefoldin in gene expression, and discuss the implications of these results for the relationship between prefoldin structure and function