Bilateral Monopolies and Incentives for Merger

We analyze a duopoly in which firms acquire inputs through bilateral monopoly relations with suppliers. We combine a bargaining model with a duopoly model to examine how input prices and profits are affected by the structures of the upstream and downstream industries, by the demand relations among the final products, and by the nature of bargaining between suppliers and firms. We find that the implications for the incentives for merger are significantly different from what they would be in an environment in which input prices are not determined in bargaining.

Evolution of binding sites for Zinc and Calcium ions playing structural roles

The geometry of metal coordination by proteins is well understood, but the evolution of metal binding sites has been less studied. Here we present a study on a small number of well-documented structural calcium and zinc binding sites, concerning how the geometry diverges between relatives, how often nonrelatives converge towards the same structure, and how often these metal binding sites are lost in the course of evolution. Both calcium and zinc binding site structure is observed to be conserved; structural differences between those atoms directly involved in metal binding in related proteins are typically less than 0.5 Å root mean square deviation, even in distant relatives. Structural templates representing these conserved calcium and zinc binding sites were used to search the Protein Data Bank for cases where unrelated proteins have converged upon the same residue selection and geometry for metal binding. This allowed us to identify six archetypal metal binding site structures: two archetypal zinc binding sites, both of which had independently evolved on a large number of occasions, and four diverse archetypal calcium binding sites, where each had evolved independently on only a handful of occasions. We found that it was common for distant relatives of metal-binding proteins to lack metal-binding capacity. This occurred for 13 of the 18 metal binding sites we studied, even though in some of these cases the original metal had been classified as essential for protein folding. For most of the calcium binding sites studied (seven out of eleven cases), the lack of metal binding in relatives was due to point mutation of the metal-binding residues, whilst for zinc binding sites, lack of metal binding in relatives always involved more extensive changes, with loss of secondary structural elements or loops around the binding site. Proteins 2008. © 2007 Wiley-Liss, Inc